Preheat oven to 375 F.
In medium mixing bowl, sift together flour, baking powder, and salt. In a large mixing bowl cream together butter, peanut butter and sugars. Add in eggs one at a time, mixing thoroughly after each addition. Add dry ingredients into peanut butter mixture, and mix thoroughly. Cover cookie dough with plastic wrap, and refrigerate 1 hour or until firm.
Using a cookie scoop or disher, portion cookie dough into 1-inch balls. Roll each ball in white sugar, and place on ungreased baking sheet. Flatten each ball with a fork dipped in sugar, making a criss-cross pattern (alternately, dip the bottom of a glass in sugar and flatten cookie). Bake in a preheated oven for about 10 minutes or until cookies begin to brown around edges. Do not over-bake.