Cut the cakes into small chunks, then place them in a large bowl along with the softened cream cheese, milk, and vanilla. Smaller pieces help distribute the frosting coating throughout the mixture rather than leaving large coated chunks.

Work the mixture with a hand mixer, moving the beaters around the bowl until the cream cheese blends evenly throughout. The finished mixture should look creamy with tiny cake and frosting flecks, not completely uniform.

Switch to a spatula and lift the cake mixture over the thawed Cool Whip repeatedly until the white ribbons disappear. A light, billowy texture signals that the whipped topping has blended in without losing its volume.

Refrigerate the dip until serving, then finish with the optional sprinkles and a whole tree cake if you have an extra. The chilled mixture should hold a soft mound, and freshly added sprinkles will keep their colors distinct.

Set the chilled dip out for serving with the dippers arranged nearby. Each scoop should be creamy and thick enough to cling without pouring off.