Step One: Crumb Coat the Cake
Place the cake on the turntable and add a thin layer of white buttercream, creating a crumb coat.
Step Two: Prepare the Frostings
Add approximately 20 drops of food coloring to one cup of buttercream for dark brown, five drops to half a cup for medium brown and three drops to have a cup for light brown. You can adjust to your reach your desired shades. You may also use chocolate buttercream instead.
Step Three: Frost the Top of the Cake
Fill a piping bag with light brown and another piping bag with medium brown frosting. Pipe a circle in the middle with medium brown buttercream. Pipe a few rings of light brown buttercream, then one of medium brown buttercream and then finish with more light brown rings.
Step Four: Smooth Out the Rings
Using the straight icing spatula, gently smooth out the rings. Position the tip of the spatula over the center and tilt the blade of spatula up. Carefully place the lower flat edge of the spatula on the buttercream and slowly spin the turntable, smoothing the lines out.
Step Five: Apply the White Buttercream
Apply a thick layer of white buttercream along the sides of the cake. Try not to let the buttercream go above the top, but it is alright if it pokes up some over the top.
Step Six: Smooth the Cake
Using the straight icing spatula, smooth the sides of the cake and around the top.
Step Seven: Pipe Dark Brown Buttercream
Pipe the sides of the cake with dark brown streaks. Pipe the streaks going horizontal around the cake, making them thin and random.
Step Eight: Smooth the Frosting
Use a flat edge to smear the brown lines on the cake. Repeat until the cake reaches the birch appearance you desire.
Step Nine: Add Finishing Touches
Use the back end of a paint brush to create a small hole that only goes through the white layer of frosting. Repeat as you feel necessary. If you wish, add buttercream leaves or carve initials into the side.
Birch tree cakes make for beautiful wedding cakes. They have a natural woodland look that many people love.