Preheat your oven to 350 degrees. Grease a round 9" baking pan or heart shaped baking pan. Set aside.
Using a stand mixer or hand mixer, beat the butter, sugars, eggs, egg yolk and vanilla on medium speed. Mix until combined.
Add the flour, baking soda and salt. Mix until incorporated.
Mix in cup of semi-sweet chocolate chips using a wooden spoon. Stir until combined.
Press the cookie dough into your pan evenly. Top cookie with a handful of milk chocolate chips or M&M's, pressing them into the top of the dough.
Bake for 22-25 minutes or until light golden brown. Remove from oven and cool on a cooling rack.
Using a stand mixer or hand mixer, beat the butter, confectioners sugar, vanilla and cream on medium speed until combined and smooth. Add in food coloring if you choose and place into a piping bag.
Once cooke cake has completely cooled, pipe along the edge of the cake using a star tip. Top the buttercream with small sprinkles.
Slice and enjoy! Store covered on the counter for up to three days.