1. In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

2. In a large mixing bowl, beat the softened butter and sugar until light and fluffy (about 2–3 minutes).

3. Mix in the egg, vanilla, lemon zest, and lemon juice until fully combined.

4. Gradually add the dry ingredients to the wet, mixing just until a soft dough forms.

5. Divide dough into two, wrap in plastic wrap, and chill for at least 1 hour.

6. Preheat oven to 350°F (175°C). Roll out dough to ¼-inch thickness on a lightly floured surface.

7. Cut into Christmas tree shapes and place on a parchment-lined baking sheet.

8. Bake for 9–11 minutes, or until edges are lightly golden. Cool completely on a wire rack.

9. In a bowl, whisk powdered sugar with lemon juice until smooth. Tint with yellow food coloring.

10. Spread icing on each cookie. Once set, drizzle with white royal icing and decorate with sprinkles.