Preheat oven to 375F. Combine butter, peanut butter, brown sugar, and white sugar until fluffy, stir in egg and vanilla, mix well. Combine flour, baking powder, baking soda, and salt in a separate bowl, add to butter mixture, mix well.
Roll dough into 1” balls, tuck a Snickers piece into each. Place on greased cookie sheet 2” apart, bake for 8-10 minutes or until light golden brown, do not overbake. Take sheet from oven, slightly flatten (gently tap) each cookie with a metal spatula, wait about 1 minute before moving to wire rack to cool. Yield: 28-30 cookies.
Easier variation: Use Snack Size Hershey Milk Chocolate bars broken into sections in place of Snickers. Do not tuck candy inside dough balls, just press into cookies as they are taken from oven.