In a small bowl, combine flour, baking soda and salt; set aside.
In a large bowl, using an electric hand mixer, beat peanut butter, butter, granulated sugar, brown sugar and vanilla extract until creamy. Add eggs, one at a time, beating well after each addition. Gradually beat in flour mixture. Stir Reese's Pieces. Cover and refrigerate dough for 1 hour.
Preheat oven to 375 degrees.
Drop by rounded tablespoon onto ungreased baking sheets. Bake for 9 to 11 minutes or until golden brown. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.
Pan Cookie: Preheat oven to 350 degrees. Grease 15 x 10-inch jelly-roll pan. Prepare dough as above. Spread into prepared pan. Bake for 20 to 25 minutes or until golden brown. Cool in pan on wire rack.