Preheat & Prep. Preheat your oven to 350°F. Lightly grease a 9-inch round cake pan (or line it with parchment if you’re feeling like a person who has their life together).

Dry Ingredients. In a bowl, whisk together flour, baking soda, and salt. Set aside.

The Good Stuff. In another bowl, mix melted butter, brown sugar, and granulated sugar until smooth and glossy. Add the egg, egg yolk, milk, and vanilla. Stir until combined.

Bring It Together. Add dry ingredients to wet ingredients and mix until just combined. Fold in chocolate chips like the domestic goddess you are.

Into the Pan. Press the dough evenly into your prepared pan. (It will feel thick—trust the process.)

Bake. Bake for 18–22 minutes, until the edges are set and the center is just slightly soft.Do NOT overbake. We are not making a cookie frisbee.

Cool completely in the pan.

Chocolate Frosting (aka The Finishing Touch That Makes It a “Cake”)

Beat the butter until creamy.

Add powdered sugar and cocoa powder, mixing slowly at first unless you enjoy cleaning sugar clouds off your counters.

Add milk, vanilla, and salt. Beat until smooth and fluffy.

If it’s too thick, add a splash more milk. Too thin? A little more powdered sugar.

Assemble

Once the cookie cake is completely cool, pipe or spread frosting around the edges (or all over if you’re feeling emotionally bold). Add sprinkles if you want that full food court birthday energy.