Preheat your oven to 350°F.

Spray a 9×13 baking dish with nonstick cooking spray.

Using a stand mixer or hand mixer, beat the butter and brown sugar together until fluffy and smooth.

Mix in the eggs and vanilla extract until fully combined.

Mix in the salt and baking powder. Add the flour one cup at a time, mixing between additions.

Stir in 1 cup pastel M&Ms. The batter will be thick—this is normal!

Spread the cookie dough evenly into the prepared pan. Tip: If the dough is difficult to spread: Wet your hands and press it into the pan or use a spatula sprayed with nonstick spray.

Add a few extra M&Ms on top for a colorful finish.

Bake for 22–25 minutes, or until the top is lightly golden brown. Be careful not to overbake, or the cookie bars may become dry.

Let the bars cool in the pan for 15–20 minutes before slicing.

Store in an airtight container with a slice of bread to keep the bars soft for 3–4 days.