1 cup butter or margarine, softened
1 cup peanut butter
1 cup firmly packed brown sugar
1 cup granulated sugar
2 eggs
1 teaspoon vanilla extract
3 1/2 cups flour
1 teaspoon baking soda
Granulated sugar

In large bowl of an electric mixer, beat butter until creamy. Gradually beat in peanut butter, then brown sugar, then granulated sugar. Beat in eggs, then vanilla extract.

In another bowl, stir together flour and baking soda; gradually add to butter mixture, blending thoroughly. Roll dough into 1-inch balls and place 2 inches apart on greased baking sheets. Press balls down with fork tines dipped in granulated sugar. Bake at 375 degrees F for 10 to 12 minutes, or until golden brown. Let cool on baking sheets for about 1 minute, then transfer to racks and let cool completely. Store airtight.