In a medium bowl add flour, baking soda, and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugars until mixture is light and fluffy, about 2 minutes. If you don’t have a stand mixer, a hand mixer works fine.
Add egg and vanilla and mix until well blended.
Add flour mixture, and beat until fully combined.
Fold ½ cup of Valentine’s Day M&Ms into cookie dough.
Add dough to a 10-inch well greased, ovenproof, cast iron skillet, and press into the bottom of the pan.
Press remaining ½ cup of Valentine’s Day M&Ms into the top of the cookie batter.
Bake 35-40 minutes, until edges are brown.
Be sure not to over bake. The cookie will continue to cook in the heavy skillet after it’s removed from the oven.
Transfer to a wire rack to cool, 15 to 20 minutes.
Cut the cookie into wedges and serve warm.
Recipe by In The Kitchen With KP at https://www.inthekitchenwithkp.com/recipes/mm-valentine-skillet-cookie