Brown the Butter:
Place the butter in a medium saucepan and melt over medium-low heat. Continue cooking, stirring frequently, until the butter turns a golden brown and gives off a nutty aroma. This should take about 5-7 minutes.
Tip: Watch it closely as it can burn easily once it starts browning. When done, remove the pan from the heat and pour the butter (and all those golden brown bits!) into a mixing bowl. Let it cool for about 5-10 minutes. This way, it wonât cook the eggs when we mix them in.
Mix in Sugars:
Once the brown butter has cooled a bit, add the brown sugar and granulated sugar. Whisk or beat on medium speed until well combined. The mixture will look a little grainy but will smooth out once we add the eggs.
Add Egg, Yolks, and Vanilla:
Mix in the whole egg, both egg yolks, and vanilla extract. The yolks add extra richness, making the cookies super chewy. Continue mixing until the texture is smooth and slightly creamy.
Fold in Dry Ingredients:
In a separate bowl, whisk together the flour, baking soda, cornstarch, and salt. Then, gradually add this dry mixture to the wet ingredients, folding it in gently. Try not to overmix, as this can make the cookies tough. You want just enough mixing for the flour to disappear.
Add M&Ms:
Gently fold in the M&Ms. If youâre using mini M&Ms, youâll get that pop of chocolate in every bite! If you like a mix of chocolate types, you could even swap half the M&Ms for mini chocolate chips.
Chill the Dough:
Cover the bowl and refrigerate the dough for about 30 minutes. Chilling helps the flavors meld together and prevents the cookies from spreading too much when baking.
Scoop and Bake M&M Cookies:
Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Use a medium cookie scoop or spoon to portion out the dough into balls, placing them a couple of inches apart.
Bake M&M cookies for 10-12 minutes, or until the edges are golden brown. The centers may look a little soft, but theyâll firm up as the cookies cool.
Cool and Enjoy:
Allow the M&M cookies to cool on the baking sheet for about 10 minutes before transferring them to a cooling rack. This makes the edges set just right while keeping the centers soft.