Preparation Steps

• Preheat oven to 350F. Line an 8x8-inch baking pan with aluminum foil and spray with cooking spray.
• Melt butter in a large microwave-safe bowl, about 1 minute on high.
• Wait a moment before adding the egg to prevent scrambling. Add egg, brown sugar, vanilla, and whisk until smooth.
• Add the flour and stir until just combined, avoiding overmixing.
• Stir in the Oreo cookies.
• Pour batter into prepared pan and smooth the top with a spatula.
• Sprinkle M&M's evenly over the top and press down lightly.
• Bake for 20-22 minutes until edges are firm and a toothpick inserted in the center comes out clean.
• Allow bars to cool in the pan for at least 30 minutes before slicing and serving.