For the filling:
- 3 tablespoons sugar
- 4 ½ teaspoons instant coffee granules
- 4 ½ teaspoons unsweetened Dutch-process cocoa powder
For the batter:
- ½ cup (1 stick) unsalted butter, softened, plus more for pan
- 2 cups all-purpose flour, plus more for pan
- 1 teaspoon baking soda
- 1 teaspoon baking powder
- 1 teaspoon salt
- 1 cup sugar
- 2 large eggs, room temperature
- 1 cup sour cream, room temperature
- 1 teaspoon pure vanilla extract
- Preheat oven to 175ºC (350ºF).
- Make the filling: stir together sugar, coffee and cocoa powder in a small bowl; set aside.
- Butter a 10-inch (12 cup) Bundt pan. Dust with flour, and tap out excess.
- Make the batter: whisk flour, baking powder, baking soda and salt in a medium bowl.
- Put the butter and sugar into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until pale and fluffy, 3 to 4 minutes. Reduce speed to medium. Mix in eggs, one at a time. Mix in flour mixture in 3 batches, alternating with sour cream. Add vanilla, and mix 1 minute.
- Spread one-third of the batter into prepared pan. Sprinkle with half the filling. Spread another third of the batter on top, followed by the remaining filling. Spread remaining batter over top. Run a thin knife through batter to marbleize.
- Bake until a cake tester inserted into center comes out clean, 35 to 38 minutes. Let cool 30 minutes.
- Invert onto a plate