Preheat oven to 350F/180C. Grease a 9 x 9-inch baking pan. Set aside

In a medium bowl, cream the peanut butter and butter. Gradually add the sugars, beating until light and fluffy.

Add the eggs, beating well after each. Blend in the vanilla.

Mix the flour, baking powder and salt. Stir into the peanut butter mixture, blending well.

Turn into prepared pan, making an even layer.

Bake 30-35 minutes or until a toothpick inserted in the center comes out clean.

Cool and cut into 9 portions.