Preheat your oven to 350°F (175°C) and line a 9x13-inch baking dish with aluminum foil, spraying it with nonstick cooking spray.

In a stand mixer, cream together the unsalted butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add the eggs and pure vanilla extract, mixing on medium speed until fully combined.

Gradually mix in the all-purpose flour, baking soda, and salt until just combined.

Fold in the M&Ms and mini chocolate chips, reserving some for topping.

Transfer the dough into the prepared baking dish and press into an even layer. Sprinkle reserved M&Ms and chocolate chips on top.

Bake for 30-35 minutes until edges are golden brown and center feels set.

Allow to cool completely in the pan on a wire rack for at least 1 hour before slicing into bars.