Begin by preheating your oven to 350 degrees. Lightly spray the inside of each mini skillet with baking spray and set aside.
Place the butter, brown sugar, and sugar in a bowl. Beat to combine. Add the eggs and vanilla extract and beat again until smooth.
Then add the flour, baking soda, and salt. Mix until just combined. Stir in the chocolate chips and M&Ms, reserving a few to press into the top of each cookie cake after baking.
Bake at 325 degrees Fahrenheit for about 30 minutes or until the edges are golden. (The center will still be slightly underbaked. The cookie cakes will continue to bake once they are removed from the oven.) Press the reserved chocolate chips and M&Ms into the top of each cookie cake.