Step 1: Prepare the Cakes

1. Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking pan or a silicone Christmas tree-shaped mold.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
3. In a large mixing bowl, cream the butter and sugar together until light and fluffy.
4. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
5. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk. Mix until just combined.
6. Pour the batter into the prepared pan or molds and bake for 20–25 minutes, or until a toothpick inserted into the center comes out clean.
7. Let the cakes cool completely before cutting or decorating.

Step 2: Make the Buttercream Frosting

1. In a large bowl, beat the softened butter until creamy.
2. Gradually add the powdered sugar, one cup at a time, mixing well.
3. Add the heavy cream and vanilla extract, then beat until smooth and fluffy. Adjust the consistency by adding more cream if needed.
4. Mix in the green gel food coloring until the frosting reaches your desired shade of green.

Step 3: Assemble and Decorate

1. If you used a flat baking pan, cut the cake into triangle shapes to resemble Christmas trees. If using molds, gently remove the cakes.
2. Frost the cakes with green buttercream using a piping bag fitted with a star tip or spatula.
3. Decorate with sprinkles to mimic ornaments, use a candy cane for the tree trunk, and lightly dust with powdered sugar for a snowy effect.
4. Let the decorated cakes set in the refrigerator for about 15 minutes before serving.