Level the cooled cake layers with a long serrated knife and choose which layer will be the bottom (tip: pick the sturdiest layer). Place it on a cake plate, turning table, or serving dish. Spread on roughly 3/4 cup of the buttercream with an offset spatula. Top with the next layer of cake and repeat, ending with the third layer (tip: pick the most level, attractive layer for the top). Frost the sides and top of the cake with the remaining buttercream. Use a straight-sided frosting spatula and bench scraper are great for producing smooth sides. Refrigerate the cake, uncovered, for 20 to 25 minute before glazing.