How to Make It
Preheat oven to 350°F. Grease and flour 3 (8-inch) cake pans.
Prepare the Cake: Beat together sugar and butter with an electric mixer on medium speed until light and fluffy, about 5 minutes. Add eggs, 1 at a time, beating well after each addition.
Whisk together flour, cocoa, baking soda, and salt in a bowl. Add to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed until just blended after each addition. Beat in vanilla. Divide batter evenly among prepared pans.
Bake in preheated oven until a wooden pick inserted in center comes out clean, about 25 minutes. Cool in pans on wire racks 10 minutes. Remove from pans; cool completely on wire racks, about 30 minutes. Trim the domes off of each cake layer; crumble trimmings, and place in a single layer on a baking sheet. If trimmings are too moist to finely crumble, place in 350°F oven until dry, 10 to 15 minutes, stirring halfway through. Cool completely, and crumble into fine crumbs. (Or use a food processor to make fine crumbs.) Reserve crumbs for garnish.
Prepare the Frosting: Beat together cream cheese and butter with electric mixer at medium speed until creamy, about 1 minute. Gradually add powdered sugar, beating until fluffy, 3 to 4 minutes. Beat in vanilla.
Spread frosting between layers and on top and sides of cake. Warm a teaspoon in very hot water. Drag tip of spoon gently around sides and top of cake, warming spoon often, to create swirls. Gently press reserved cake crumbs into bottom 2 to 3 inches of cake. Sprinkle cake crumbs around 1-inch edge on top of cake. Store covered in refrigerator up to 5 days.