In a large mixing bowl, beat the peanut butter and butter with an electric mixer for 30 seconds. Add the packed brown sugar, granulated sugar, baking powder, and baking soda. Beat on medium speed until mixture is fluffy.
Add the eggs and the vanilla; beat well. At low speed, beat in the flour. With a wooden spoon, stir in the rolled oats and the raisins or chocolate.
Using 1/4 cup dough for each cookie, drop the dough 3 inches apart on greased cookie sheets. Press the dough into 4-inch circles.
Bake the cookies in a 375 degree F oven for about 10 minutes or until the edges are golden. Let the cookies stand for 1 minute. Transfer the cookies to wire racks to cool. Makes 16 to 18 large cookies.