Design Eat Repeat

0 Preheat oven to 350°F.
1 Roughly chop [adjustable]½[/adjustable] cup of chocolate chips using a knife, rolling pin, or meat mallet (if not using a knife, place chips in a plastic bag while crushing). The goal here is to have a mixture of tiny chocolate flakes throughout the dough, while still have the whole chunks in there for texture. Once chopped, set aside.
2 Warm the unsalted butter ([adjustable]½ cup, i.e. 1 stick[/adjustable]) in a microwave-safe bowl or saucepan until it’s just melted. 
3 Combine the melted butter with the light brown sugar ([adjustable]½ cup) and granulated sugar (¼ cup[/adjustable]) in a mixing bowl and use a wooden spoon or spatula to stir them together (*do not use a mixer!).
11 Next, stir in the egg ([adjustable]1[/adjustable] large) and vanilla extract ([adjustable]2 teaspoons), followed by the baking soda (½ teaspoon) and salt (½ teaspoon[/adjustable]). 
12 Mix in unsweeteend cocoa powder ([adjustable]½ cup) and all-purpose flour (1 cup[/adjustable]) until well-combined, then stir in chocolate chips (the full [adjustable]1 cup[/adjustable] of the chopped & whole).
4 Immediately spread dough into a greased cookie cake pan (you don't want the dough sitting out or it will set too much with the melted butter).
6 Bake at 350°F for 12-14 minutes or until cookie cake looks “rippled” and the center no longer looks super wet (see photo in post above!). Cool completely before frosting.
7 Using a large star piping tip, pipe around the edges then immediately add sprinkles (the frosting will start hardening quick, so add sprinkles right away!).
To Make Frosting:
10 Beat the softened unsalted butter ([adjustable]½ cup), vanilla extract (2 teaspoons), and salt (¼ teaspoon[/adjustable]) on medium-high speed for 1 minute until smooth.Turn the mixer to low speed then slowly add the unsweetened cocoa powder ([adjustable]½ cup) and powdered sugar (2 cups[/adjustable]). You may need to stop and scrape down the sides. Add milk, as needed to develop a pipeable consistency ([adjustable]2-3 [/adjustable]tablespoons total).Beat on high for 1-2 minutes until creamy and the frosting is at a good consistency to pipe. If it looks too runny, add more powdered sugar. If it looks too stiff, add another tablespoon  of milk until you get to the desired consistency. This will make just enough frosting to pipe a generous border along the edges.