Preheat oven to 350 degrees F. Grease or place parchment paper on two baking sheets.
In a medium bowl, mix together flour, baking soda, and salt. Set aside.
With an electric mixer, cream butter and sugars until light and fluffy. Add egg and vanilla and beat until well combined. Add peanut butter and mix just until combined.
Add flour half at a time and mix. Stir in Reese’s pieces.
Scoop tablespoons of dough onto baking sheet 2 inches apart. Bake 10-12 minutes until slightly golden brown on edges.