Preheat oven to 350°F (177°C). Line a baking sheet with parchment paper.
Cream together butter, granulated sugar, and powdered sugar until light and fluffy (2–3 mins).
Add in the egg, vanilla extract, and optional sour cream. Mix until smooth.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Slowly add dry ingredients to wet ingredients. Mix until a soft, non-sticky dough forms.
Scoop large balls of dough (about 3 tbsp each), roll them smooth, and flatten slightly (they won’t spread a lot).
Bake for 10–12 minutes, or until edges look set and the center is still soft. Don’t overbake! Let them rest on the sheet for 5 minutes before transferring.