Preheat oven to 350°F (180°C). Spray 2 (9-inch) round cake pans with baking spray with flour. Line bottom of pans with parchment paper.

In a 2-cup glass measuring cup, whisk together coffee and cocoa until completely combined. Let stand until mostly cooled, about 30 minutes.

In the bowl of a stand mixer, beat brown sugar and eggs at high speed until light and fluffy, stopping to scrape sides of bowl. Add mayonnaise, and beat until combined.

In a large bowl, sift together flour, baking soda, salt, and baking powder. With mixer on low speed, gradually add flour mixture to sugar mixture alternately with coffee mixture, beginning and ending with flour mixture, beating just until combined after each addition. Divide batter between prepared pans.

Bake until a wooden pick inserted in center comes out clean, 28 to 35 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks.

Level cooled cake layers, if desired; discard parchment. Place a cake layer on a cake plate. Spread 1½ cups (412 grams) Creamy Chocolate Frosting on cake layer; top with remaining cake layer. Spread remaining frosting on top and sides of cake.