Preheat the oven to 375 degrees. Cream the butter, white sugar, brown sugar, soda, salt, peanut butter, and vanilla. Gradually add the flour until blended well. Shape the dough into 1 inch balls and place on a greased cookie sheet. Bake 10-12 minutes depending on the size of balls you make. After baking immediately add an unwrapped chocolate kiss in the center of each cookie. (This is optional)