- 6 TBS (3/4 stick) unsalted butter
- 2/3 cup Dutch-processed cocoa powder
- 2 ounces bittersweet or semisweet chocolate, chopped
- 1/3 cup packed light or dark brown sugar
- 1 cup granulated sugar
- 3/4 cup all-purpose flour
- 2 tsp baking powder
- 1/3 cup whole milk
- 1 TBS vanilla extract
- 1/4 tsp salt
- 1 large egg yolk, at room temperature
- 1 1/2 cups coffee, at room temperature (see note above)
DirectionsPreheat oven to 325 degrees F. Lightly coat an 8-inch-square glass or ceramic baking dish thoroughly with vegetable oil spray.
Melt the butter, 1/3 cup of cocoa, and the chocolate together in a medium bowl in the microwave, whisking often, until smooth, 1 to 3 minutes. In a separate bowl, stir the brown sugar, 1/3 cup of the granulated sugar, and remaining 1/3 cup cocoa together until there are no clumps. Whisk the flour and baking powder together in a third bowl.
Whisk the remaining 2/3 cup granulated sugar, milk, vanilla, and salt together in a large bowl. Whisk in the yolk, then the chocolate mixture until combined. Whisk in the flour mixture until combined.
Spread the batter in the prepared baking dish. Sprinkle the brown sugar mixture evenly over the batter. Pour the coffee gently over the brown sugar mixture. Bake until the cake is puffed and bubbling and just beginning to pull away from the sides of the baking dish, about 45 minutes, rotating the pan halfway through baking. (Do not overbake.)
Let the cake cool in the dish on a wire rack for about 25 minutes before spooning into bowls.