First, in a large bowl or the bowl of a stand mixer, cream butter until light and fluffy. Use an electric hand mixer or a stand mixer fitted with the paddle attachment.
Add in granulated sugar and brown sugar and continue mixing until well incorporated. Add in vanilla and egg and continue mixing.
In a separate medium bowl whisk together flour, baking powder and salt.
Gradually add the dry ingredients to the butter mixture mixing after each addition until all of the flour mixture is incorporated.
Place the dough in the center of a piece of wax paper or parchment paper form into cylinder with a diameter of about 2 inches. Wrap the dough log in wax or parchment paper and place it in the refrigerator for at least an hour before baking.
When your dough has chilled and you are ready to bake preheat the oven to 350 and line a cookie sheet with parchment paper or a silicone mat.
Using a sharp knife slice the dough in 1/4 inch to 1/2 inch slices place them on the prepared baking sheet about 1-2 inches apart.
Bake for 10-14 minutes or until the edges are a light golden brown and the center appears dry.
Allow to cool on the baking sheet for 2-3 minutes before moving to a wire rack to cool completely.
Store the cooled cookies in an airtight container.