Preheat your oven to 350 degrees Fahrenheit. This step is crucial for ensuring your bars bake evenly and develop that perfect golden crust.
Lightly grease a 9x13 baking dish or line it with parchment paper. This will make it easy to remove the bars once they’re baked.
In a large mixing bowl, cream together the butter and brown sugar until the mixture is light and fluffy. You’ll know it’s ready when it turns a light color and has a smooth texture.
Beat in the flour and salt until the mixture becomes nice and crumbly. You want a texture that holds together but is still crumbly enough to sprinkle over the top later.
Reserve ¾ cup of the crumb mixture and press the remaining mixture firmly onto the bottom of the prepared baking dish. This will form the base layer of your bars.
Bake the crust for 10 to 12 minutes or until it turns golden brown. Keep an eye on it to ensure it doesn’t over-bake; we want that perfect crust!
While the crust is baking, combine the sweetened condensed milk and bittersweet chocolate chips in a microwave-safe dish. Heat in the microwave on medium for 30 seconds at a time, stirring in between, until the chips are completely melted and the mixture is smooth.
Pour the melted chocolate mixture over the hot crust and spread it evenly to cover the surface. This creates a luscious layer that will melt in your mouth.
Sprinkle the Andes chips on top of the chocolate layer, ensuring even coverage. This will add flavor and a beautiful visual appeal.
Sprinkle the reserved crumb mixture over the chocolate mixture, followed by the semi-sweet chocolate chips and mint M&Ms. This layering creates a delightful texture and flavor contrast.
Bake for an additional 25 to 30 minutes or until the bars are set. The center should be firm but still have a little give to it.
Once baked, allow the bars to cool completely in the dish before cutting them into squares. Patience is key here; it’ll be worth the wait!