Preheat the oven to 375℉. Line 2 baking sheets with parchment paper and set aside.

In the large bowl of an electric standing mixture, beat together the butter, peanut butter, sugar, and brown sugar until well mixed. Slowly beat in the eggs.

In another bowl, stir together the flour, baking powder, and salt. Slowly add the dry mixture to the peanut butter mixture, using the lowest mixer setting. Mix until the ingredients are just blended. Don't overheat. Put the bowl with the dough in the refrigerator to chill for 1 hour.

Roll the dough into 1" balls and place on the baking sheet, about 2" apart. Press down on each ball with a fork, making a criss-cross pattern. Bake the sheets separately, for 8-10 minutes, until the edges are set and the middle is no longer shiny. Remove the pan from the over and allow the cookies to cook on the baking sheet for 10 minutes before removing the cookies and placing them on a baking rack to cool. Bake the second sheet while the first is cooling and repeat the process,

Allow the cookies to cool completely before storing them in an airtight container in the refrigerator.