Place peanut butter & butter in mixer bowl. Attach bowl & flat beater to mixer. Turn to speed 6 and beat until mixture is smooth, about 1 minute. Stop & scrape bowl. Add sugars, egg & vanilla. Turn to speed 4 and beat about 1 minute. Stop & scrape bowl.
Turn to stir speed. Gradually add all remaining ingredients to sugar mixture and mix about 30 seconds. Turn speed to 2 and mix about 30 seconds.
Roll dough into 1-inch balls. Place about 2 inches apart on ungreased baking sheets (I use parchment paper on the baking sheets)Press flat with fork in a criss-cross pattern to 1/4 inch thickness.
Bake at 375 degrees until golden brown, about 10-12 minutes. Remove from baking sheets immediately and cool on wire racks.