Either support the sandwiched cake layers in the palm of one hand or set them on a heavy-duty turntable. (Two-layer cakes larger than 8 inches require the turntable.)
Use a metal spatula to place a large gob of frosting on a side of the cake. Press it from side to side without lifting away the spatula so that it doesn’t lift away any crust. Continue all around the cake layer, allowing the frosting to rise about ¼ inch above the top.
Frost the top of the cake in the same way as the top of the first layer. When the entire surface is covered, hold the spatula halfway across the cake with the blade almost flat against the frosting. Pressing lightly, rotate the turntable in one full circle.