1. Prepare the Crust:

1. Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
2. In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the egg and vanilla extract.
3. In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add to the wet ingredients, mixing until a dough forms. Add green food coloring and mix until the color is uniform.
4. On a lightly floured surface, roll out the dough to about 1/4-inch thickness. Use Christmas tree-shaped cookie cutters to cut out shapes. Place cookies 1 inch apart on the prepared baking sheets.
5. Bake for 7-9 minutes, or until the edges are just beginning to turn golden. Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.
6. Once completely cool, decorate the cookies with royal icing or melted white chocolate to create garlands and ornaments, then add sprinkles and candies.