Preheat oven to 325 degrees.

In a 10 or 12 inch cast iron skillet, melt butter over medium heat stirring often, until it starts to bubble and is completely melted. Turn heat to low and add sugar and brown sugar, stirring well, until the mixture is well combined.

Remove from the heat and let the mixture cool for 5 minutes.

Stir in the eggs and vanilla.

Stir in flour, baking soda, and salt.

Add 1 cup of the M&M's candies and stir to combine. Smooth the top of the cookie in the pan. Drop the rest of the M&M's on top of the cookie so that they just rest on the top and look pretty.

Bake at 325 degrees for 25 to 35 minutes or until the edges are golden brown. The center of the skillet cookie will have a crust but will still be gooey underneath; the edges will be crisp. The smaller pan will cook for more time and a larger skillet will cook for less time.

Top with vanilla ice cream and eat while still warm.