Preheat the oven to 180C / 350F and line an 8×8 baking pan with parchment paper.
In a mixing bowl, mix together sugar and butter until light and fluffy. Mix in eggs and vanilla extract until combined.
1 cup brown sugar, ⅗ cup butter, 1 teaspoon vanilla extract, 2 eggs
Stir in flour, baking powder, and salt until incorporated.
1 ¾ cups all purpose flour, 1 teaspoon baking powder
Finally, fold in M&Ms, Oreos, and chocolate chips. Spread the batter evenly in the baking pan.
½ cup chocolate chips, ½ cup Christmas M&M's, 7 Oreos
Bake for 30-35 minutes, let it cool, and cut it into squares.
Notes
Don't overbake it; otherwise, it will crack and come out dry.
These blondies can be kept at room temperature for 1-2 days. If you want to extend their shelf life, keep them in the fridge for 3-4 days. You may also freeze them for 1-2 months.