Melt butter in a cast iron skillet. Remove from heat and pour butter into a large mixing bowl. Add sugar and vanilla and mix well. Stir in eggs. Add flour, baking soda, salt and mix until combined. Fold in ½ cup chocolate chips.
Spoon batter into skillet and sprinkle with remaining 2 tablespoons chocolate chips and m&m candies.
Bake for 22-28 minutes or until edges are golden brown.