Spray the bottom of a springform pan or glass pie dish with cooking spray.
Mix cookie mix, butter and egg in mixer or with a beater until a soft dough forms.
Stir in sprinkles if desired.
Put dough in baking pan and pat into a level layer.
Bake at 325 for about 35 minutes, checking near the end of baking time. Cookie is done when set in the middle and edges begin to brown.
Cool completely before icing