Step 1: Preheat your oven to 350°F (175°C).
Step 2: In a large mixing bowl, combine the sugar cookie mix, softened butter, and egg. Blend until smooth and well combined.
Step 3: Spread the cookie dough in your greased baking pan. Bake for 15-18 minutes, until edges are golden brown.
Step 4: In a separate bowl, beat the cream cheese until smooth. Add one box of pudding mix and 1 cup of cold milk; mix until creamy.
Step 5: Add the remaining 2 cups of cold milk and whisk until thickened and smooth.
Step 6: Gently fold in the thawed whipped topping into the mixture.
Step 7: Once the cookie base has cooled, pour the cream cheese and pudding mixture over the top.
Step 8: Sprinkle your choice of festive sprinkles over the top.
Step 9: Refrigerate for at least 2 hours to set. Slice into squares and serve chilled.