n the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter on medium-high speed until light and fluffy, about 3 minutes. Scrape down the bowl and paddle. With the mixer on low, gradually mix in the flour until a smooth dough forms.

Turn out onto a lightly floured work surface and knead the dough gently to form a ball. Divide the dough in thirds, wrap each in plastic or waxed paper, and flatten into squares. Refrigerate at least 4 hours or overnight.

Position a rack in the center of the oven and heat the oven to 400F. Line 3 cookie sheets with parchment. Remove one piece of dough from the refrigerator and roll it out on a lightly floured surface into a 1/8-inch-thick rectangle. Using a sharp knife or a pizza cutter, trim the rough edges of the dough so the sides are straight, and then cut into 2-inch squares. Spoon about 1/2 tsp. of the preserves onto the center of each square. Fold one corner into the center, dab with the beaten egg, and then bring the opposite corner into the center and pinch firmly together to seal the corners. With a thin spatula, transfer the cookie to the cookie sheet. Repeat the process with the remaining dough.

Bake one sheet at a time until golden and very lightly browned and puffed, 10 to 12 minutes. Transfer to a rack to cool completely and then dust with confectioners? sugar.