I have made a large chocolate chip cookie with M&M’s sprinkled on top prior to baking many times. It is actually a family favorite. The cookie was delicious. The M&M’s adhered to the top without noticeable shifting.
The recipe can be found in The Lodge Cast Iron Cookbook (Rose has a recipe in that book http://www.realbakingwithrose.com/2012/02/the_gold_standard_of_cast_iron.html#.Vhkyhdb_FFI )
Here is the recipe:
1 cup firmly packed light brown sugar
1/2 cup granulated sugar
1 cup (2 sticks) unsalted butter, softened
1 teaspoon vanilla extract
2 large eggs
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
2 cups chocolate chips
Assorted M&M’s or sprinkles
1. Preheat the oven to 375°.
2. In a large bowl, using an electric mixer, beat both sugars and the butter until smooth. Beat in the vanilla. Add the eggs, one at a time, beating well after each addition. Add the flour, baking soda, and salt. Stir well with a wooden spoon. The dough will be stiff. Stir in the chocolate chips.
3. Spray a 10-inch cast iron skillet with cooking spray. Pat the cookie dough evenly into the skillet and decorate the surface with M&M’s or sprinkles. Bake until the edges are lightly browned, about 30 minutes.
4. Remove the skillet from the oven and let cool on a wire rack for 15 minutes. Cut the cookie into 16 wedges and serve it directly from the skillet using a pie server.