01 -
Preheat oven to 350°F. Generously spray two 9-inch round baking pans with non-stick baking spray and set aside
02 -
In a stand mixer with paddle attachment or large bowl with electric mixer, combine both sugars, flour, cocoa, baking soda, baking powder and salt on low until thoroughly combined
03 -
In another large bowl, whisk together eggs, yolk, sour cream, milk, oil and vanilla until well combined
04 -
Add wet ingredients into dry ingredients and beat on low until just incorporated. Carefully add hot coffee or water and beat until completely combined, about 1 minute. Batter will be thin
05 -
Divide batter evenly between pans. Bake for 30-32 minutes, until toothpick inserted in center comes out clean or with few moist crumbs
06 -
Cool cakes in pans on cooling rack for 10 minutes before removing and transferring to rack to cool completely
07 -
Place chopped chocolate in heatproof bowl over barely simmering water. Heat, stirring frequently, until completely melted. Remove from heat and set aside to cool slightly
08 -
Beat butter until creamy. Gradually add confectioner's sugar on low speed, one cup at a time, beating well after each addition
09 -
Once all sugar is added, increase speed to medium-high and beat for 2 minutes. Beat in vanilla and melted chocolate until well combined and creamy
10 -
Level cake tops with serrated knife. Place one layer on plate, spread thick layer of frosting on top, then add second layer. Frost top and sides of cake
11 -
Decorate with chocolate chips, sprinkles, chocolate shavings as desired, or leave plain