Preheat oven to 350 degrees. Spray a 9x9 pan with nonstick cooking spray.
Heat butter in a saucepan over medium-low heat until it turns an amber color and begins to smell nutty. Brown bits will start to appear in the bottom of the pan.
In a large bowl, stir together the browned butter and sugars. With a wooden spoon, stir in the egg, vanilla, heavy whipping cream and salt. Stir in flour, semi-sweet chocolate chips and half of a cup of the M&M's. Spread evenly into the pan and sprinkle with the remaining M&M's. Gently press them into the batter.
Bake for 25-30 minutes (recommended 27 minutes). Let the blondies cool completely on a wire rack. Cut into squares and store in an air-tight container.
Notes
Makes 16 bars.
Recipe by DessertedPlanet.com at https://dessertedplanet.com/valentine-mm-blondies/