Heat oven to 350F. Grease a 9x13" pan and line with parchement for easy removal. I cut a long strip that only goes up the ends of the dish. Set aside.

In a large bowl of a standup mixer beat butter with both sugars on medium speed until fluffy. Beat in peanut butter, eggs and vanilla. Turn the mixer to low and add the flour and baking powder slowly. Stir in the Reese's mini pieces.

Spread the dough into the prepared pan and bake for 30-35 min. or until set and golden brown. Cool completely in pan on a cooling rack for about 1 hour. Cut down the edges of the long side of the pan. Using the parchment paper carefully pull the blondies out. Place onto a cutting board. Cut the long side into 6 slices and then each slice into four pieces. Store in an airtight container. Freezes well also.