Cream butter and sugar: In a large bowl, beat butter and sugar until light and fluffy (3-5 minutes).
Add wet ingredients: Mix in the egg and vanilla until fully combined.
Combine dry ingredients: In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Mix wet and dry: Gradually add dry ingredients to the wet mixture, mixing just until dough forms.
For soft, thick cookies: Roll dough into 1-inch balls, slightly flatten, and place on a parchment-lined baking sheet. Chill for 15 minutes in the fridge. Bake at 350°F (175°C) for 12 minutes or until the edges are slightly golden.
For cut-out cookies: Roll dough to ¼ inch thickness on a floured surface. Use cookie cutters in desired shapes (hearts, Christmas trees, pumpkins). Chill cut-outs for 15 minutes before baking to maintain shape. Bake at 350°F (175°C) for 8-10 minutes.