Step 1

Preheat oven to 350 degrees. Line baking sheets with parchment paper or silicone liners.

Step 2

In a mixing bowl whisk together flour, baking soda, baking powder and salt, set aside.

Step 3

In the bowl of an electric stand mixer cream together butter and sugar until well combined.

Step 4

Mix in egg, egg yolk and vanilla.

Step 5

Add in flour mixture and mix just until combined. If cookie dough seems very soft chill for 1 hour before proceeding so cookies spread less.

Step 6

Scoop dough out using a medium cookie scoop (or 1 1/2 Tbsp at a time, and roll into balls if not using a cookie scoop) and drop onto baking sheet, spacing them 2-inches apart.

Step 7

Bake in preheated oven 9 - 11 minutes, they should appear slightly under-baked. If baking two batches at once then rotate pans halfway through baking.

Step 8

Cool on pan 5 minutes then transfer to a wire rack to cool completely.

Step 9

Store cookies in an airtight container.