Combine brown sugar, butter eggs and vanilla in a large mixing bowl. Add flour, baking powder, baking soda and salt. Fold in candy. Line a 9-inch square baking dish with parchment paper. Press dough into pan.
Bake in a 350 degree oven for 35-40 minutes. Remove and cool completely. Cut into 16 bars.
Notes
If you’d like more of the M&M’s to be inside the blondies, put ¾ cup of M&M’s into the batter, then sprinkle the remaining ¼ cup on top. I actually did half and half because some M&M’s sink into the batter while cooking and this shows more of them on the top.
Store: I keep my cut blondies bars in an airtight container at room temperature. They'll last about a week, but mine always disappear within a day or two because we love them so much.
Can you freeze blondies? Yes! These bars freeze beautifully. Cut into bars, then freeze with sheets of wax paper between layers of bars to keep them from sticking together. Let thaw and enjoy.