50gdark chocolate, for piping a message (optional)
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Instructions
Cookie Cake
Preheat oven to 350°F and line the bottom of a 8" cake pan with a circle of parchment paper.
In a large bowl, beat butter with a hand mixer or stand mixer until it becomes smooth and creamy. Mix in brown sugar and granulated sugar until well combined. Add eggs and vanilla extract and mix until creamy.
In a medium bowl, stir together flour, baking soda, baking powder, and salt. Add this dry mixture to the wet mixture and fold together with a spatula until almost combined.
Add in the rainbow sprinkles and fold until just incorporated.
Smooth the batter into your lined cake pan. Don't worry about getting all the way to the edges as it will fill the pan as it bakes. Bake at 350°F for 23-25 minutes or until the top has set and edges are golden brown.
Let cool for at least 10 minutes before removing from pan. The middle will sink as it cools.
Vanilla Buttercream Frosting
In a mixing bowl, beat softened butter with a hand mixer or stand mixer for about 5 minutes until light, fluffy, and creamy.
With the mixer on low, add in the powdered sugar and vanilla extract. Add in milk as needed, one tablespoon at a time, until the buttercream becomes smooth, creamy, and pipeable.
Pipe buttercream on top of the cake and write a message with melted chocolate, if desired.