Make the cake: Heat oven to 350 degrees F. Lightly coat two 8-inch cake pans with softened butter. Cut two 8-inch circles out of parchment paper and fit them into the bottom of the cake pans. Lightly coat the paper circles with butter. Lightly flour both pans, shake out excess flour and set aside. Beat the cake mix, cocoa, mayonnaise, eggs, and water in a large bowl with an electric mixer set on low speed. Increase speed to high and beat for 2 more minutes. Pour batter into prepared pans and bake until a toothpick inserted into the middle comes out clean — about 35 minutes. Cool cakes in pans on wire racks for 20 minutes. Remove cakes from pans and return to the wire racks until completely cool.
Make the filling: Whisk the frosting, sour cream, and vanilla together in a large bowl. Transfer 1 1/2 cups of frosting to a medium bowl and stir in the almonds and the toasted coconut. Set aside.
Assemble the cake: Split both layers and brush away any excess crumbs. Place one split layer on a cake plate. Tuck strips of wax paper under the edges of the cake to protect the plate. Spread 1/3 of the filling over the layer. Top with the next layer and spread another 1/3 of the filling over the top. Repeat with the third cake layer and remaining filling and top with the final cake layer. Spread the frosting over the top of cake smoothing out to the edges. Spread the remaining frosting around the sides and serve or store covered for up to 4 days.