I got this recipe out of my mother's Spririt of Christmas Cookbook. I always use the smooth peanut butter since we don't keep the crunchy on hand and it comes out just fine.
In a bowl combine butter and sugars. Add eggs and vanilla and beat until smooth. Combine the dry ingredients in a bowl. Add to butter mixture and stir until moistened. Stir in peanut butter.
Spread in a greased 7x11-inch greased baking pan.
Bake 20 to 25 minutes or until it is set in the center. Cool completely and cut in squares.