Mix cake according to manufacturer’s instructions. Measure out 3 pounds batter, deposit 1 pound into a sprayed and papered 8-inch cake pan. Repeat two times to make 3 cakes total. Bake at 350F until cake springs back lightly when touched. Let cool completely.
Once cooled, trim the bellies of each cake, saving them for other uses. Then split each layer in half to make 6 layers total, save one later for another use. Place one cake round on a cake board, pipe velvatop around the edges. Using a #12 green scoop, place one scoop keylime filling on the cake round and spread to edges and place another cake round on top. Repeat with the next layers, giving the cake 5 layers and topping with keylime filling. Place internal supports/dowels into the cake. Using a piping bag fitted with an open French star tip, pipe velvatop around the top edges of the cake and sprinkle with toasted coconut.