How To: Holiday Sprinkle Cake Roll out fondant measured to size of the cake.Use cookie cutter to cut the outlines (set them aside) Now place the fondant on the cake & trim the top piece to level out the line. Now fill in with sprinkles as needed! Get creative! Add little ones and big ones - in a symmetrical way too! You can add the extra cut fondant as decor as well! Add details of fondant & top decor!