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.