For the cake:
Cooking spray
2 cups all-purpose flour
1 cup granulated sugar
1 (4-ounce) package instant chocolate pudding
1 teaspoon baking powder
1 teaspoon baking soda
1 cup sour cream
4 large eggs
1/2 cup vegetable oil
1 teaspoon vanilla extract
For the cola frosting:
8 tablespoons (4 ounces) unsalted butter
1/2 cup cola soda
1/4 cup natural unsweetened cocoa powder
2 cups powdered sugar
1/2 teaspoon vanilla extract
Make the cake: Arrange a rack in the middle of the oven and heat to 350°F. Coat a 9x13-inch baking dish with cooking spray.
Whisk the flour, sugar, pudding mix, baking powder, baking soda, and salt together in a large bowl; set aside. Whisk the sour cream, eggs, oil, and vanilla together in a medium bowl.
Add the wet mixture to the dry mixture and stir to combine; a few lumps are more than fine. Pour the batter into the prepared pan and spread into an even layer.
Bake until a tester inserted in the center of the cake comes out clean, 20 to 22 minutes. Set on a wire rack to cool slightly while you make the frosting.
Make the frosting: Place the butter, cola, and cocoa in a small saucepan over medium heat and, stirring occasionally, bring to a boil. Remove from the heat and stir in the powdered sugar and vanilla until smooth. Pour over the still-warm cake and cool for at least 30 minutes before serving.
Recipe Notes
- Pudding substitute: You can replace store-bought chocolate pudding mix with 2/3 cup granulated sugar, 1/3 cup natural unsweetened cocoa powder, and 3 tablespoons cornstarch.