01 -
Heat oven to 350°F. Line baking sheets with parchment paper.
02 -
Whisk flour, baking powder, baking soda and salt until well combined.
03 -
Beat butter and sugar until light and fluffy, about 2 minutes. Mix in egg, yolk and vanilla.
04 -
Add dry ingredients to wet. Mix on low just until combined.
05 -
Roll into 1-inch balls. Coat in sugar if desired. Place 3 inches apart on sheets.
06 -
Bake one sheet at a time for 8-9 minutes until tops are barely set. Don't overbake.