Wednesday, December 5, 2012

Opera Cake

-ingredients-
For almond sponge cake
  1. 3 tablespoons cake flour (not self-rising), sifted after measuring, plus additional for dusting pan
  2. 2 whole large eggs at room temperature for 30 minutes
  3. 1 cup almond flour (3 1/2 oz) or 2/3 cup blanched whole almonds (see cooks' note, below)
  4. 1/2 cup confectioners sugar, sifted after measuring
  5. 2 large egg whites at room temperature for 30 minutes
  6. 1/8 teaspoon cream of tartar
  7. 1/8 teaspoon salt
  8. 1 tablespoon granulated sugar
  9. 2 tablespoons unsalted butter, melted, foam discarded, and butter cooled

For coffee syrup
  1. 1 teaspoon instant-espresso powder
  2. 1/2 cup plus 1 tablespoon water
  3. 1/2 cup granulated sugar
  4. 1/4 cup Cognac or other brandy

For coffee buttercream
  1. 2 teaspoons instant-espresso powder
  2. 1/4 cup plus 1 tablespoon water
  3. 6 tablespoons granulated sugar
  4. 2 large egg yolks
  5. 1 stick (1/2 cup) unsalted butter, cut into 1/2-inch cubes and softened

For chocolate glaze
  1. 3/4 stick (6 tablespoons) unsalted butter
  2. 7 oz fine-quality bittersweet chocolate (not unsweetened; preferably 70 to 71% cacao), coarsely chopped

Special equipment: a 15- by 10-inch shallow baking pan; an offset metal spatula; a candy thermometer; a small sealable plastic bag
-preparation-

Make sponge cake:
Put oven rack in middle position and preheat oven to 425°F. Butter baking pan, then line bottom with a sheet of parchment or wax paper, leaving a 1-inch overhang on short sides, and generously butter paper. Dust pan with cake flour, knocking out excess.
Beat whole eggs in a large bowl with a handheld electric mixer at high speed until eggs have tripled in volume and form a ribbon when beaters are lifted, 2 to 3 minutes. Reduce speed to low, then add almond flour and confectioners sugar and mix until just combined. Resift cake flour over batter and gently fold in.
Beat egg whites in a bowl with cleaned beaters at medium speed until foamy. Add cream of tartar and salt and beat until whites just hold soft peaks. Add granulated sugar, then increase speed to high and beat until whites just hold stiff peaks.
Fold one third of whites into almond mixture to lighten, then fold in remaining whites gently but thoroughly. Fold in butter, then pour batter evenly into baking pan, spreading gently and evenly with offset spatula and being careful not to deflate (batter will be about 1/4 inch thick).
Bake until very pale golden, 8 to 10 minutes, then cool in pan on a rack 10 minutes.
Loosen edges of cake with spatula, then transfer cake (on paper) to a cutting board. Cut cake into strips and squares. Trim outside edges slightly, then carefully peel paper from strips and squares and set back on paper.
Make coffee syrup:
Stir together espresso powder and 1 tablespoon water until powder is dissolved. Bring sugar and remaining 1/2 cup water to a boil in a 1- to 2-quart heavy saucepan, stirring until sugar is dissolved. Reduce heat and simmer syrup, without stirring, 5 minutes. Remove from heat and stir in Cognac and coffee mixture.
Make coffee buttercream:
Stir together espresso powder and 1 tablespoon water until powder is dissolved. Bring sugar and remaining 1/4 cup water to a boil in a very small heavy saucepan, stirring until sugar is dissolved. Boil, without stirring, washing down any sugar crystals on side of pan with a pastry brush dipped in cold water, until syrup registers 238°F on thermometer (soft-ball stage; see cooks' note, below).
While syrup boils, beat yolks in a large bowl with cleaned beaters at medium speed 1 minute.
Add hot syrup to yolks in a slow stream (try to avoid beaters and side of bowl), beating, then add coffee mixture and beat until completely cool, 3 to 5 minutes. Beat in butter, 1 piece at a time, and beat until thickened and smooth.
Make glaze:
Melt butter and all but 2 tablespoons chopped chocolate in a double boiler or in a metal bowl set over a saucepan of barely simmering water, stirring occasionally, until smooth. Remove top of double boiler and stir in remaining 2 tablespoons chocolate until smooth, then cool glaze until room temperature but still liquid.
Assemble cake: 
So at long last we get around to the Opera cake tutorial I’ve been meaning to put up for a week. What can I say, I’m easily distracted by food science. And chocolate, well, it’s terribly interesting stuff. You’ll thank me for all those posts later, I promise you.
Well…maybe not.
So anyway, Opera cake. If at all possible, I suggest that you make up all your various components on one day, then build the cake the next. Because let’s face it, it’s easy to get worn out over the course of a lengthy baking or cooking project. Enthusiasm wanes with time and impatience sets in, and that opens the door to potentially catastrophic mistakes. Separating the stirring and baking phase from the building phase not only gives you a breather, it makes the assembly a whole lot more pleasurable. All the components including the joconde will keep just fine at room temperature overnight.
Begin by trimming the edges off your two joconde sheets. Once that’s done, measure them and cut them in half. The exact dimensions are less important than making sure they’re all the same size. You want four layers, which is traditional for an Opera cake. You want the “up” side of the joconde layers (when they were finished baking) to remain their “up” side, as they’re more porous and will more easily absorb the syrup.
 Job one is to apply a thin scraping of melted chocolate to the underside of the bottom layer. Remove it to a separate sheet of parchment, flip it over and spread the good stuff on. Let it firm for a few minutes, then place it in the refrigerator for a few more. What will this do? Besides adding still more deliciousness, it will ensure that the cake doesn’t stick to the cake board when it’s time to slice and serve. (This is an excellent, consequence-free opportunity to practice your tempering, should you be so inclined). 
Flip it over onto your cake plate or cake board, chocolate side down (here again I’m going traditional and using a decorated board).
Gently peel the parchment back, center it on the board and you’re ready to go. 
 First thing, apply coffee syrup to your layer, and don’t be shy about it. I know what I’ve said about cake syrup in the past: it’s overused. However in this context you really want to go hog wild. Thoroughly soaking the layer will give the cake the melt-in-the-mouth texture that Opera cakes in Paris are known for. Pastry chef Camille, who works in a Paris pâtisserie and makes these cakes regularly, tells me the layers should be soaked until they’re brown all the way through. So no genteel paintings of syrup. Go Jackson Pollock on the sucker. 
And now for your first layer of buttercream. Take your time, and pay special attention to the edges. As with all icing and/or topping jobs, the tendency will be to pile all the good stuff up in the middle. Spread the buttercream slowly and deliberately, eyeballing it from all sides to get it as even as you can. You want it about a quarter inch thick.
Apply your next layer of cake. 
Soak it.
Now it’s time for your middle layer of ganache. Oh yeah. Spread it thinner than the buttercream. Just a covering will do.
Apply the next layer of joconde.
Do I need to tell you what to do?
Another quarter-inch layer of coffee buttercream. Again, check for evenness all the way around as you apply it.
 Then the top layer of cake. Edges getting a little sloppy? Don’t worry, you’ll trim those off later. Check again for evenness. If you have any obviously high spots, it’s OK to press them down a little with your palm at this point.
Soak, soak, soak.
And now for the top. Here you want just a thin scraping of buttercream, mostly to fill in any pits so the tempered chocolate top will lay on smoothy. Now’s a good time for a beer break, if you were wondering.
Prepare your tempered chocolate according to the tutorial. Or, if you just want to melt some bittersweet chocolate and put it on, that’s fine too (if you’ve gotten this far, you’ve already done one heck of a job). Spread it on promptly and thinly
Let the chocolate firm at room temperature for about ten minutes. Then, using a knife you’ve heated under hot tap water (then dried) slice off the edges to reveal the layers. (Keep and hide those trimmings, kids. The pastry chef deserves a secret, greedy coffee break sometime in the next day or two).
Looks pretty good. Maybe not an Opera cake for the ages, but pretty darn decent.
Once that’s done it’s time to score the top so it doesn’t shatter later when you want to cut it. Again, heat a long knife under hot tap water, dry it, and do your business.
Pieces can be any size you like. Here I’m dividing the cake into eight. As rich as this cake is, these pieces are huge. Ten would have been better, but oh well.
Now’s the time to put your Opera cake in the refrigerator while you nip on down to the corner store for a little edible 23-karat gold.
What.
Edible gold. You get it at the Quick Mart. Second shelf on the right next to the oatmeal. What sort of neighborhood do you live in? I’ll admit it’s tricky stuff to handle. You don’t want to touch it with your fingers, since it’ll stick and disintegrate when you try to peel it off. I use two x-acto knives as implements to cut and steady it, then just transfer pieces — of whatever shape — over to the cake. Not very elegant, but gold makes a statement whatever shape it’s in.
Your Opera cake can now be refrigerated for a day or two if need be. Opera cake is best slightly chilled. Ideally not refrigerator-cold, maybe an hour or so out of the fridge. When you’re ready to serve, separate the pieces (again with a warm knife) and transfer to plates. Ah yes, the chocolate-on-the-bottom trick worked splendidly, did it not?

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