Preheat the oven to 350 degrees. Prepare baking sheets with parchment paper.
Melt the butter in the microwave for about 30 seconds or until it is just melted. Allow it to cool slightly at room temperature. Set aside.
In a large bowl, sift together flour, baking soda, and salt. Set aside.
In a stand mixer, beat the melted butter, granulated sugar, and brown sugar for about 2 minutes, until well blended and creamy.
Add vanilla and the egg, then beat on low speed for about 10 seconds, just until incorporated.
Add flour, baking soda, and salt. Mix the dry ingredients until just incorporated into the wet ingredients. Turn off the mixer and remove the bowl.
Using a wooden spoon (or your hands!) gently fold in the chocolate chips/chocolate chunks and the M & Ms to the mixture.
Form 2-inch balls (I use a large cookie scoop) and place on prepared cookie sheets lined with parchment paper, about 2 inches apart, as these will spread.
I add a few chocolate chunks and M & Ms to the tops of each cookie so that when they bake, they stand out of the cookie a bit (see baked cookie pics), but this step is completely optional.
Bake for 10-13 minutes at 350°F, just until the edges are slightly browned but the centers are still soft and slightly puffy (but not jiggly). Cool on cooling racks for 10 minutes before devouring. Enjoy!
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