Preheat oven to 350F (175C) and line the bottom of two 8” baking pans (see note for different size pans) with cut-out parchment paper lines and spray the sides with baking spray (or you may thoroughly grease and flour the pans). Set aside.
In a medium-sized saucepan, combine butter, milk, water, cocoa powder, and instant coffee.
1 cup unsalted butter, ½ cup whole milk, 1 cup water, ¾ cup Dutch-process cocoa powder, 1 teaspoon instant coffee
Place on stovetop over medium-low heat and stir frequently until butter is melted. Increase heat to medium and bring to a boil, stirring constantly. Remove from heat and allow to cool for 15 minutes while you prepare the dry ingredients.
In a separate large bowl whisk together flour, sugar, baking soda, baking powder, and salt.
2 cups all-purpose flour, 1 cup granulated sugar, 1 cup light brown sugar, 1 ½ teaspoons baking soda, 1 teaspoon baking powder, 1 teaspoon salt
Whisk the chocolate mixture briefly once more to combine then Pour into flour mixture. Stir until smooth.
Add sour cream and stir until combined.
¾ cup sour cream
Add eggs and vanilla and stir well until batter is smooth.
2 large eggs, 2 teaspoons vanilla extract
Evenly divide batter into prepared baking pans and bake on 350F (175C) for 30-35 minutes or a toothpick inserted in the center comes out clean or with fudgy crumbs (preferred, as sometimes a clean toothpick can indicate the cake is overdone).
Allow to cool in the baking pans for 15 minutes then run a knife along the edge to loosen it from the pan and carefully invert onto a cooling rack to cool completely (be careful, the pans will still be hot).
Cool completely before frosting.
1 batch chocolate frosting
Video
Notes
Coffee
Instead of using water and instant coffee you can instead just use 1 cup of your favorite coffee. The coffee enriches the chocolate flavor of the cake and I recommend it, but if you have neither coffee nor instant coffee the recipe can be made with just water (it'll still be good!).
Baking Pans/Making as Cupcakes
This recipe may be baked in two 9” pans (bake for 28-30 minutes) or it will make 24 cupcakes (bake for 17-18 minutes).This recipe will also work in a 9x13" pan baked for approximately 30 minutes. Always use the toothpick test to check for doneness: a toothpick inserted in the center should come out clean or with moist, fudgy crumbs (preferable).A bundt pan will also work though I have not tried this recipe in a bundt pan myself so cannot comment on the bake time.
Making In Advance
You may make the cake up to two days in advance of frosting and serving. Simply bake and cool then wrap tightly in plastic wrap. I store at room temperature.This cake may be prepared, cooled, and frozen for up to a month before thawing and frosting. After frosting, the cake may be stored in an airtight container at room temperature for up to 48 hours or in the refrigerator for up to 5 days.