Preheat oven to 350°F. Line a 9x13-inch pan with foil and spray with nonstick cooking spray.

Place melted butter in a large bowl. (You can also use a stand mixer fitted with the paddle attachment or a hand mixer.) Add granulated and brown sugars and stir until the mixture is smooth. Stir in egg and vanilla extract and stir until combined.

Mix in baking soda and salt, then slowly mix in flour and mix just until the batter is smooth and comes together. Be sure to scrape the sides of the bowl during mixing. Slowly mix in chocolate chips.

Press batter in the bottom of prepared pan.

Spread sweetened condensed milk over the cookie dough, leaving a ½ inch border around the edges of the pan. Place peanut butter cups on top the milk.

In a medium bowl, whisk cinnamon, salt, baking soda, and flour. Set aside.

Cream butter and sugar in the bowl of a stand mixer fitted with the paddle attachment. (You can also use a large bowl and a hand mixer.) Cream until smooth, about 1-2 minutes. Mix in eggs and vanilla, beat until smooth.

Gradually mix in dry ingredients until smooth, being careful not to over mix. Add oats and mix, then stir in M&Ms.

Drop spoonfuls of the dough over the top of the peanut butter cups in prepared pan and lightly press to flatten and cover the top (some areas won’t be totally covered).

Bake 30-38 minutes, or until light golden and no longer glossy. Cool completely before slicing into bars. (It’s easiest to slice these when they are cold.)

Store in an airtight container for up to 4 days or freeze for up to 3 months.