1: Preheat oven to 350°F (177°C). Prepare a 12-inch round metal pan or 9-inch springform pan by spraying with nonstick spray and lining the bottom with parchment paper. For easier removal and even baking, a springform pan is recommended.

2: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cornstarch. Set aside.

3: In a large bowl, beat softened butter with sugar on medium speed for about 20-30 seconds (do not overbeat), until creamy but not fluffy. Add egg and egg yolk, then vanilla and almond extracts, mixing until combined.

4: Gradually add the dry ingredients in three parts, mixing on low speed just until incorporated to avoid overmixing.

5: Fold in sprinkles and white chocolate chips carefully if using avoid overmixing to prevent color bleed and keep the cookie tender.

6: Press the dough evenly into the prepared pan. If the dough is sticky, place another piece of parchment paper on top and smooth it out by pressing.

7: Bake for 25 to 35 minutes depending on pan size and dough thickness. The edges should be lightly browned, and the center may still look slightly underbaked and soft.

8: Allow the cookie cake to cool completely in the pan. For springform pans, cool about 10 minutes before releasing the sides, then cool fully before frosting.

9: To make the frosting, beat the softened butter on medium speed until light and creamy (about 2 minutes). Gradually add powdered sugar while continuing to beat. Add vanilla, almond extract, milk or cream, and a pinch of salt if desired. Beat on high for 2-3 minutes until fluffy and spreadable. Adjust consistency by adding more milk/cream or powdered sugar as needed.

10: Spread frosting evenly over the fully cooled cookie cake. Use a piping bag with a star tip to pipe decorative borders if desired. Immediately decorate with sprinkles or other toppings before the frosting sets.