Design Eat Repeat

0 Preheat oven to 350°F.
2 In a small microwave-safe bowl, melt unsalted butter ([adjustable]1[/adjustable] stick, [adjustable]½[/adjustable] cup) for 30-45 seconds until fully melted (no chunks). 
3 Add in light brown sugar ([adjustable]½[/adjustable] cup) and granulated sugar ([adjustable]¼[/adjustable] cup) and use a spatula to stir until combined (* do not use a mixer). 
11 Add egg ([adjustable]1[/adjustable] large) and vanilla extract ([adjustable]2[/adjustable] teaspoons), then mix.
12 Add baking soda ([adjustable]½[/adjustable] teaspoon), cinnamon ([adjustable]½[/adjustable] teaspoon), and salt ([adjustable]½[/adjustable] teaspoon), then mix until combined. Add all-purpose flour ([adjustable]1 ½[/adjustable] cups) and mix until all the flour disappears into the dough.
5 Grease a 11.5" metal cookie cake pan (don't have one? See notes below). Although this cookie removes cleanly, if you are worried about it sticking, line the bottom and sides of the pan with parchment paper first. Use a spatula or your (greased) hands to press down the dough into a smooth layer (being sure to get all the corners).
13 Mix the topping by combining the granulated sugar ([adjustable]3[/adjustable] tablespoons) and cinnamon ([adjustable]¾[/adjustable] teaspoons) in a small bowl. Sprinkle on top of the cookie cake until fully covered, then shake off any excess.
6 Bake at 350 degrees for 12-14 minutes - do NOT overbake or your chocolate chip cookie cake will not be soft. You want the cookie cake to be slightly brown on the top and look slightly underbaked (my oven was perfect at 12 minutes). Remove from oven and place entire pan on a cooling rack. Allow the cookie cake to cool completely before removing.Tip: To remove from pan, use a knife to go around the edges, place a flat platter on top, then flip over the pan to remove. If you used parchment paper, this should come out rather smoothly. After flipping over the cookie cake, flip it over again on the final decorate plate or platter (I LOVE these cute paper trays and the largest one in the pack is perfect for a 10" cookie cake).
To Make Frosting:
14 Beat the softened unsalted butter ([adjustable]½[/adjustable] cup, i.e. [adjustable]1[/adjustable] stick) on medium-high speed for 2 minutes until smooth.
15 Turn the mixer to low speed then add the powdered sugar (¼ cup at a time, [adjustable]2½[/adjustable] cups total). You may need to stop and scrape down sides.
16 Add vanilla extract ([adjustable]2[/adjustable] teaspoons), salt ([adjustable]⅛ [/adjustable]teaspoon) and cinnamon ([adjustable]¼[/adjustable] teaspoon) turn mixer to medium speed. One tablespoon at a time, add milk ([adjustable]2[/adjustable]-[adjustable]3[/adjustable] tablespoons). Beat on high for 2-3 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 a tiny bit of milk until you get to the desired consistency.
Frost Cookie Cake
17 Once cookie cake has cooled completely, use a large star piping tip to pipe around the edges then immediately add sprinkles (the frosting will start hardening quick, so add sprinkles right away!).If you're feeling fancy, you can double the frosting recipe to have enough to pipe phrases like "Happy Birthday" on the top. Or use this fool-proof letterboard cake topper kit (these are made from plastic so you can wash and reuse for years!).