Chocolate lovers, rejoice! The rich flavor of chocolate is right at home in this delicate chiffon cake. Not only does dark cocoa enhance the cake itself, it enriches the decadent cream filling inside. A dollop of lightly sweetened whipped cream on each slice balances the flavors and makes an elegant presentation.
To make the cake: Preheat the oven to 325°F with a rack in the bottom third. Have on hand an ungreased 10" tube or angel food cake pan.
In a large bowl, beat the egg whites with the cream of tartar until foamy. Gradually add 1/2 cup (99g) of the sugar and continue beating until stiff and glossy. Set aside.
In a medium bowl, whisk together the remaining 1 cup (198g) sugar with the flour, cocoa, baking powder, and salt.
In a large bowl beat the oil, reserved egg yolks, and vanilla until pale yellow; use your machine's whisk attachment if you're using an electric mixer.
Add about one-third of the flour mixture, followed by half the buttermilk, another one-third of the flour, the remaining buttermilk, and the rest of the flour, whisking until each is combined before adding the next. When done, whisk at medium speed for 2 minutes.
Gently fold in the whipped egg whites with a whisk or spatula, mixing just until the batter is thoroughly combined. Scrape the bottom of the bowl to ensure everything is mixed in. Pour the batter into the prepared pan.
To bake the cake: Bake the cake for 50 minutes without opening the oven; it will rise high above the pan then settle back almost even with the rim as it continues to bake.
Increase the oven temperature to 350°F and bake for 10 minutes more, until a gentle touch on the center of the cake leaves no mark; if you listen carefully, the cake should make a crackling sound.
Remove the cake from the oven and invert the pan over the neck of a wine bottle or other long-necked bottle for 30 minutes. After 30 minutes, use a thin-bladed flexible spatula to free the cake from the sides and center tube of the pan. Turn the cake out onto a serving plate to finish cooling completely.
To make the filling: Place the heavy cream in a large mixing bowl, preferably the bowl of a stand mixer fitted with a whisk attachment. Sift the confectioners' sugar and cocoa on top. Stir together, then whip until soft peaks form.
Add the vanilla and salt, and continue to whip until medium peaks form.
To assemble the cake: Using a large, sharp serrated knife, cut a 1" slice off the top of the baked cake and reserve it.
Slice a tunnel out of the middle of the cake, leaving a 1" wall on the sides and bottom. (Reserve the hollowed-out cake for another use, or enjoy as a baker's snack.)
Fill the tunnel with the filling, then place the top back on the cake and refrigerate until ready to serve.
To serve: Sift confectioners' sugar or cocoa over the cake, then slice. Top each slice with a spoonful of whipped cream or garnish with berries, if desired.
Storage information: Store leftover cake, well wrapped, in the refrigerator for a couple of days. Freeze the unfilled cake, well wrapped, for up to a month; thaw and fill just before serving.
Separate the eggs carefully; even a small amount of yolk in the whites will prevent them from beating up properly. The eggs separate most easily when cold, but allow them to come to room temperature before mixing, for best volume in the egg whites.
Chiffon cake maintains its beautifully soft texture even when chilled, making it a great candidate for any type of filling or topping that needs refrigeration, e.g., whipped cream, pastry cream, or mousse.
Looking for other flavors of chiffon cake? Check out our recipes for Lemon Chiffon Cake, as well as our classic Chiffon Cake, with hints of vanilla and almond.
