MOCHA BUTTERCREAM AND MOCHA PASTRY CREAM

Mocha Buttercream and Mocha Pastry Cream image

A filling of custardy pastry cream is layered within the Mocha Bubble Cake. Ultra-smooth buttercream adds a rich finishing touch.

Provided by Martha Stewart

Time 3h5m

Yield Makes 4 cups each (enough for one 8-inch layer cake)

Number Of Ingredients 16

Ingredients

2 tablespoons instant espresso powder
2 tablespoons hot water
4 large egg whites, room temperature
1 1/4 cups sugar
3 sticks unsalted butter, room temperature, cut into small pieces
5 ounces semisweet chocolate, coarsely chopped, melted and cooled
2 1/2 teaspoons instant espresso powder
2 1/2 teaspoons hot water
2 large eggs, plus 2 large egg yolks
1/2 cup sugar
1/2 cup whole milk
1/2 vanilla bean, split and scraped, pod reserved for another use
1/4 cup plus 1 1/2 teaspoons cornstarch
Salt
1 1/2 tablespoons unsalted butter, cut into small pieces
1 1/2 ounces bittersweet chocolate, coarsely chopped

Steps:

Make the mocha buttercream: Combine espresso powder and hot water in a small bowl; stir until espresso dissolves. Heat egg whites and sugar in a heatproof bowl of a mixer set over a pan of simmering water, whisking until whites are warm to the touch and sugar dissolves, 2 to 3 minutes. (Mixture should feel smooth when rubbed between 2 fingers.) Whisk egg-white mixture with a mixer on medium-high speed until stiff, glossy peaks form and mixture cools completely, about 10 minutes.
Reduce speed to medium-low. Add butter, a few tablespoons at a time, whisking well after each addition. Switch to the paddle attachment, and reduce speed to low. Beat in espresso mixture and melted chocolate until smooth, then beat to reduce air bubbles, 3 to 5 minutes. Cover with plastic wrap, and let stand at room temperature until ready to use.
Make the mocha pastry cream: Prepare an ice-water bath. Combine espresso powder and hot water in a small bowl; stir until espresso dissolves. Whisk eggs, egg yolks, and 1/4 cup sugar in medium bowl.
Bring remaining 1/4 cup sugar, the milk, vanilla seeds, cornstarch, and 1/4 teaspoon salt to a boil in a medium saucepan over medium-high heat, whisking constantly. Remove from heat, and gradually whisk one-third of hot-milk mixture into egg mixture. Whisk entire mixture back into saucepan. Raise heat to medium-high, and bring to a boil, whisking constantly. Cook, continuing to whisk, until mixture is thick enough to hold its shape when lifted with a spoon, about 3 minutes.
Remove from heat. Whisk in butter, 1 piece at a time. Whisk in espresso mixture and chopped chocolate until smooth. Strain mixture through a fine sieve into a bowl. Cover with parchment or plastic wrap, pressing it directly on surface to prevent a skin from forming. Transfer to ice-water bath; let stand until cooled, about 30 minutes. Refrigerate until chilled and firm, at least 2 hours.