Once the layer cakes have cooled completely, use the white batch of the Mint Swiss Meringue buttercream to assemble the cake. Use around ⅔ cup of frosting between each cake layer, and cover the cake with a smooth, thin layer of frosting. You’ll likely have a lot of buttercream leftover—this is ideal, as you’ll need this later in the decorating process. Transfer to the refrigerator to chill for at least 1 hour to allow the buttercream to set.
Once the buttercream has set, remove from the refrigerator. Cover the bottom half of the cake with green batch of buttercream, and the top half of the cake with the remaining white buttercream. Use an offset spatula to smooth the frosting around the cake completely.
Use tweezers to carefully apply a small tear of gold leaf at the border where the green and white buttercream meet. As you place the gold leaf on the cake, the gold leaf will wrinkle to give the cake the kintsugi effect. Continue tracing the border of the two colors with gold leaf until complete.