Step 1

Prep: Start by preheating the oven to 350°F. Then spray an 8-inch springform pan with nonstick spray and set aside.

Step 2

Batter: Next, in a large mixing bowl, beat the butter, brown sugar, and sugar until light and creamy. I find this easiest to do with an electric mixer or KitchenAid mixer. After that, add in the egg, egg yolk, and vanilla extract; continue to mix for 1 minute.

Step 3

Proceed to stir in the flour, cornstarch, and baking soda and mix again until combined. Then stir in the chocolate chips until just combined, be careful not to overmix.

Step 4

Bake: Spread the cookie dough into the prepared springform cake pan and top with the M&M candies, gently pressing them into the top. Bake for 20-25 minutes, until golden brown. Let the cookie cool for about 20 minutes, then run a knife around the edge and release the springform pan.

Step 5

Frosting: Prepare the icing by combining the butter, vanilla extract, and powdered sugar, mixing until the mixture is light and fluffy. Again, using an electric mixer helps greatly with this step.

Step 6

Then pipe the frosting around the edges of the cake and top with sprinkles. Slice into wedges, serve and enjoy!