Avocados in a frosting? Stick with us. They give it a rich depth of flavor, especially when paired with chocolate. We matched this unusual frosting to this cake because we loved the rich flavor and supercreamy texture that frosting brought to the dense cake, similar to the flourless chocolate cakes popular in so many restaurants. Unfortunately, the frosting won’t keep long on the cake, so plan on serving this one the day you make it. Feel free, of course, to mix and match the cake to any frosting in the book that suits your taste. Or use this vegan frosting on any egg-free, dairy-free cake in the book for a vegan dessert.
For the cake
10 tablespoons (1¼ sticks) unsalted butter, cut into small chunks, plus additional for the sheet pan
12 ounces chopped bittersweet chocolate or bittersweet chocolate chips
8 large eggs, separated, at room temperature
1 cup granulated white sugar
1 cup heavy cream
½ cup unsweetened cocoa powder
¼ cup cornstarch
1. Position the rack in the center of the oven. Heat the oven to 350°F. Generously butter the inside of a 13 × 18-inch lipped sheet pan.
2. Set the chocolate and butter in a medium saucepan over low heat and melt, stirring quite often, until smooth. Do not let the mixture bubble. Set aside off the heat and cool to room temperature, about 30 minutes, stirring once in a while.
3. Put the egg whites in a dry large bowl. Using a handheld electric mixer or a stand mixer with the whisk attachment, beat at low speed until foamy, then at high speed until you can make droopy peaks. Beat in the sugar at high speed 1 tablespoon at a time. Continue beating until you can make glossy, firm peaks.
4. Whisk the egg yolks and cream in a second large bowl until smooth and even a little light, about 3 minutes. Whisk in the cocoa powder and cornstarch until dissolved, about 1 minute.
5. Using a silicone spatula, fold in the melted chocolate mixture until uniform. Then fold in half the beaten egg white mixture until smooth. Add the remaining egg white mixture and fold in wide, gentle arcs, just until incorporated (although there may be white streaks in the batter). Using an offset spatula, spread the batter evenly into the prepared pan.
6. Bake until puffed and set, and until a toothpick or cake tester inserted into the center of the cake comes out clean, about 20 minutes. Cool in the pan on a wire rack to room temperature, about 1½ hours.
For the frosting
4 very ripe, soft avocados, peeled and pitted
⅔ cup unsweetened cocoa powder
½ teaspoon vanilla extract
½ teaspoon salt
3 to 4 cups confectioners’ sugar
1. Using a flatware fork or a potato masher, mash the avocados in a large bowl until smooth (no lumps at all, about like baby food). Stir in the cocoa powder, vanilla, and salt. Scrape down and remove the utensil.
2. Add 3 cups of the confectioners’ sugar. Whisk until thick and smooth, adding more confectioners’ sugar in 2-tablespoon increments until the mixture is spreadable and can hold its shape on the whisk. Using an offset spatula, spread and smooth the frosting over the cooled cake.
TESTER NOTES
Since the cake is gluten-free, its structure will be created almost entirely by air—that is, both by whisking the egg yolks with the cream and by beating the egg whites with the sugar. The more air you can get into these mixtures, the more tender the final crumb of the cake.
