1Start with one cup of melted and then cooled butter.
2Add one cup of brown sugar, half a cup of regular sugar, and half a teaspoon of salt.
3Whisk these all together.
4Add two room temperature eggs plus one egg yolk, whisking after each egg.
5Once eggs are mixed in, add one tablespoon of vanilla extract and mix.
6Switch to a silicone spatula and add two and a half cups of all purpose flour, making sure to fluff the flour before scooping.
7Sprinkle one teaspoon of baking soda and one teaspoon of cornstarch on top of the flour.
8Mix until almost no flour spots remain and the cookie dough has a peanut butter-like texture.
9Fold in two cups of semi-sweet chocolate chips.
10Prepare a Wilton 12-inch pizza pan by spraying it with nonstick cooking spray.
11Transfer all the cookie dough into the pan.
12Take a piece of wax paper or parchment paper sprayed with Pam, and press the dough out flat in the pan.
13Bake in a 325 degree oven for about 15 to 18 minutes (or until golden, about 26 minutes).
14Leave the cookie cake in the pan and let it cool completely.
15For the frosting, whip one stick of room temperature softened butter until fluffy, light, airy, and almost white (about two minutes).
16Add about a teaspoon of vanilla and a pinch of salt if using unsalted butter.
17Add two cups of powdered sugar and two to three tablespoons of milk, adding one tablespoon of milk at first and mixing slowly.
18Add another tablespoon of milk if the frosting looks dry and crumbly.
19Once the frosting reaches the desired consistency, whip it on high for about 30 seconds.
20Take a little bit of the vanilla frosting and put it in a separate bowl.
21To the separate bowl, add a tablespoon or two of cocoa powder and mix it up.
22Optionally, add a little bit of black cocoa to the chocolate frosting.
23Once the cookie cake is completely cool, go around the edges with a butter knife to loosen it.
24Decorate the cookie cake by making alternating dollops of vanilla and chocolate frosting around the edge, using three in a row as a guide for spacing.