Preheat oven to 350°F. Spray a regular sized muffin tins with cooking spray.
Whisk together flour, baking soda, and salt, set aside.
Beat butter and peanut butter until smooth.
Add sugars and beat on med-high until pale and fluffy (approx. 2-3mins). Reduce speed and add egg and vanilla. Beat until combined.
Add flour mixture and mix until just combined.
Using a large cookie scoop (3 Tbsp), scoop dough into muffin tins, press down to flatten slightly.
Bake for 10-12 mins or until lightly browned and mostly set.
Remove from oven and immediately use a small jar or container to press firmly down in the center to create a well. Cool in pans for 10 mins, then place on wire rack to cool completely.