This Rainbow Macaron Cake is filled with my classic vanilla buttercream and decorated with the cutest sugar daisies. A macaron is a sandwich cookie with a creme base which is made with egg whites, almond flour, confectioners’ sugar, and food coloring. Fillings like buttercream, ganache, and jam with a fruit base are common. The marshmallows are flat on the bottom, smooth on top, and have ruffled edges.