Preheat the oven to 350°F (175°C). Grease and line your cake pans with parchment paper, then lightly flour them.
In a bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, ginger, and nutmeg. Set aside.
In a large mixing bowl, beat the butter and sugars together until light and fluffy, about 3–4 minutes.
Add the eggs one at a time, mixing well after each addition. Beat in the vanilla extract.
Mix in the sour cream and applesauce until fully combined.
Add the dry ingredients in two batches, mixing just until incorporated. Do not overmix.
Divide the batter evenly between prepared pans and smooth the tops.
Bake for 22–26 minutes, or until a toothpick inserted into the center comes out clean.
Let cakes cool in the pans for 10 minutes, then turn out onto a wire rack and cool completely.
Once cooled, cut the cakes into tree shapes using a knife or template.
Beat butter for the frosting until smooth, then gradually add powdered sugar. Mix in vanilla, salt, and cream until fluffy.
Add green gel food coloring and mix until the desired shade is reached.
Apply a thin crumb coat to each cake and refrigerate for 10–15 minutes.
Frost the cakes fully, using a spatula or piping bag to create texture.
Decorate as desired, then chill briefly before serving to set the frosting.
