Preheat oven to 375ºF, and in a large bowl blend the margarine, brown sugar, and confectioners sugar until it is fluffy, and add the egg, peanut butter, and vanilla, and combine until it is smooth.
Use a medium bowl and mix the flour and baking soda, and add to the peanut butter mixture, and stir in the peanuts just until it is blended.
Drop the dough by rounded spoonfuls onto a baking sheet coated with nonstick cooking spray, and flatten each round with the back side of a fork two times (making a cross pattern), and bake for 10 to 12 minutes, or until it is lightly browned. Remove to a rack. Let cool.