Using a stand or hand mixer, mix together cake mix, instant pudding, water, oil, and eggs. Mix until well combined.
Add 1 cup of your M&Ms and fold into mixed batter. Pour into a greased baking dish and then top with remaining M&Ms.
Bake for 25-28 minutes or until cooked through and golden brown around the edge. (Time can vary depending on the brand cake mix you buy, bake according to the box instructions if they differ.)