• Preheat the oven to 350°F. Grease and line a 9x13 pan with parchment.
• In a large microwave-safe bowl, melt ½ cup unsalted butter for 20 to 30 seconds, until fully melted.
• Add ½ cup light brown sugar and ¼ cup granulated sugar and mix until combined. Add 1 large egg and 2 teaspoons vanilla extract, then stir.
• Stir in the ½ teaspoon baking soda, ¼ teaspoon baking powder, and ¼ teaspoon kosher salt. Add the 1 ½ cups all-purpose flour and stir until combined. Fold in 1 cup semi-sweet chocolate chips.
• Press the dough evenly into the prepared pan. Bake at 350°F for 12 to 14 minutes, until slightly brown on top and slightly underbaked in the center.
• Cool completely. For clean slices, cool in the pan, then chill in the fridge for 30 minutes before cutting.

To make frosting

• Beat the softened ½ cup unsalted butter on medium-high speed for 2-minutes until smooth. Turn the mixer to low speed then slowly add 2 ½ cups powdered sugar. You may need to stop and scrape down sides. Add 2 teaspoons vanilla extract and a pinch kosher salt and turn mixer to medium speed. One tablespoon at a time, add 2 to 4 Tablespoons milk. 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.

To Decorate

• Lift the cooled cookie cake out of the pan using the parchment.
• Cut the rectangle in half lengthwise so you have two long strips. Cut each strip into triangles by slicing on the diagonal, alternating the direction of your knife. You should get 14 wedges. A diagram is provided in the blog post above.
• Pipe the pink frosting across the wide top of each triangle, leaving about 1" of the straight edge bare. Next, pipe a thin line of white frosting just below the pink (a Wilton 10 tip works well). Finish the top edge with a ruffled band of green frosting using a Wilton 32 tip.
• Press a few brown mini M&M's into the pink frosting.
• Store in an airtight container for 2-3 days. This is best eaten within 2 days for best freshness.