Line an 8x8-inch baking dish with parchment paper and lightly spray it with nonstick spray. Set it aside.

Add the all-purpose flour to a small microwave-safe bowl. Microwave for 1 minute. Allow the flour to cool completely. Once the flour is completely cooled, sift the flour to remove any small clumps.

Add 1 cup of the plain M&M’s and ½ cup of the mini M&M’s to quart-size Ziploc bags. Place both in the freezer while making the rest of the recipe.

Using a medium-sized mixing bowl and a handheld mixer, cream the butter, granulated sugar, light brown sugar, half and half, vanilla extract, and salt for 1½-2 minutes.

Reduce the mixer speed to low, add the flour, and mix just until the ingredients are well incorporated. Set it aside.

In a heat-safe medium-sized bowl, heat the white chocolate chips and sweetened condensed milk in the microwave for 30 seconds at a time, stirring well after each 30 seconds, until the chips are completely melted and smooth.

Remove the Ziploc bags from the freezer. Using a wooden spoon, stir the frozen M&M’s into the butter and flour mixture.

Spoon the white chocolate mixture into the cookie dough. Stir just until all ingredients are combined.

Spoon the cookie dough fudge into the prepared baking dish.

Evenly sprinkle the remaining M&M’s and mini M&M’s on top of the cookie dough fudge. Very gently press the M&M’s into the top of the fudge. Cover tightly and refrigerate for at least 2 hours to overnight.

Remove the fudge from the refrigerator and slice the fudge into 25 squares, 5 pieces across and 5 pieces down.