Stir the flour, baking soda, and salt together, blending well, and set aside. In a large mixing bowl, beat the butter and peanut butter together for 30 seconds. Add the sugars and beat until fluffy. Add the egg and vanilla, beating well. Add the dry ingredients and blend well. Shape the dough into 3 cm balls and place on ungreased cookie sheets. Press in a crisscross pattern using a fork and flattening the balls. Bake in a preheated 190ºC . oven for about 10 minutes. Yield: About 4 dozen cookies