First, preheat your oven to 350 degrees and line a baking sheet with parchment paper.
Pour melted butter into a mixing bowl. Add to that, white sugar and brown sugar. Mix the ingredients until combined.
Add vanilla extract to bowl and crack in an egg. Whisk to blend everything together.
Now it's time to add in the dry ingredients. Measure out flour, baking soda, and salt. Drop into bowl and stir to blend together.
Add all but 2 Tablespoons of the M&M's to the cookie batter. Stir gently to incorporate.
Using a spoon, scoop round balls of dough out of the bowl and shape into about 10 cookies on the parchment paper. Use your fingers to gently press the tops and flatten them. Then add the remaining M&M's to the surface of the raw cookies.
Bake cookies for 11 minutes.
Then pull them out of the oven and allow them to cool for 30 minutes. Now they're ready to enjoy!