In a large mixing bowl, cream together the cream cheese, butter, and milk until the mixture is smooth, light, and fluffy, about 4 minutes with an electric mixer on medium-high speed.

Add the egg yolks, sugar, and 1 1/2 teaspoons vanilla extract and beat to incorporate well.

Combine the flour and baking powder in a medium bowl (my father-in-law insisted on sifting them together, but I will admit that I am pretty lazy and I never sift!)

Add the flour to the creamed mixture in 2 or 3 batches, beating to incorporate after each addition.

Once the dough comes together in a tacky blob, turn it out onto a sheet of plastic wrap. Wrap the ball of dough up in the plastic and chill in the refrigerator for at least 1 hour (you can leave it in the fridge for up to 3 days).

Preheat the oven to 400ºF.

On a lightly floured board, roll the dough out to 1/4-inch thickness.

Using a 2-inch round pastry or cookie cutter, cut the dough into rounds. Arrange the rounds about 2 inches apart on a large baking sheet (you'll likely need to bake 2 batches).

Using your thumb or another implement, press a dimple into the middle of each round.

In a small bowl, mix together the poppy seed filling, prune butter if using, and the remaining 1 1/2 teaspoons of vanilla extract.

Spoon about 1 teaspoon of filling into the center of each dough round, filling the dimple you made.

Bake for about 12 minutes, until the pastries puff up and turn golden brown. Remove from the oven and transfer to a wire rack to cool completely.