Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.

Whisk flour, baking powder, and salt in a bowl until combined.

In a separate large bowl, cream the softened butter and granulated sugar until light and fluffy — about 2–3 minutes.

Beat in the egg and vanilla until smooth.

Gradually add the dry ingredients to the wet, mixing until a soft dough forms. If the dough feels too dry, add milk 1 teaspoon at a time.

Flatten dough into a disk, wrap in plastic, and chill for 30 minutes.

On a lightly floured surface, roll dough to about 1/4 inch thickness. Cut shapes with cookie cutters.

Bake for 8–10 minutes until edges are set and just beginning to brown. Let cool for 5 minutes, then transfer to a wire rack to cool completely.

For the frosting, beat softened butter until creamy, then gradually add powdered sugar, vanilla, and milk until you reach a spreadable consistency.

Frost cooled cookies and decorate as you like.