Preheat oven to 350℉.

In a large microwave-safe bowl, melt the butter (½ cup) for 20-30 seconds, or until fully melted.

Using a spatula, stir in the light brown sugar (½ cup) and granulated sugar (¼ cup) until combined. Add the egg (1 large) and vanilla extract (2 teaspoons), then stir.

Stir in the baking soda (½ teaspoon), baking powder (¼ teaspoon), and salt (¼ teaspoon). Add the all-purpose flour (1 ½ cups) and stir until combined. Fold in the chocolate chips (1 cup).

Drop chunks of dough into a greased and parchment-lined 9x13" pan, then use a spatula or your hands (sprayed with nonstick cooking spray) to smooth it out.

Bake at 350°F for 12-14 minutes, or until it looks slightly brown on top and slightly underbaked in the center. Remove from the oven and place the pan on a cooling rack. Allow the cookie cake to cool completely before removing from the pan.

To cut into trees, use the diagram below. This is also on page 16 of my cookbook.

With an electric mixer, beat unsalted butter (½ cup) on medium-high speed for 1 minute until smooth and creamy (if using a stand mixer, use the paddle attachment). Gradually add powdered sugar (2 ½ cups), vanilla extract (1 teaspoon), and pinch of salt, mixing on low speed. Add milk one tablespoon at a time (2-3 tablespoons total), then beat on high for 2-3 minutes until creamy. Adjust the consistency with more powdered sugar or milk if needed.

For decorating, reserve ¼ cup of the frosting and color it yellow. Fit a piping bag with a star tip to pipe the stars, then color the remaining frosting green. Add sprinkles right away, as the frosting sets quickly.