Beat 6 ounces cream cheese, 1/3 cup sugar, 2 egg yolks, 2 tablespoons sour cream and 1/4 teaspoon each vanilla and salt with a mixer until smooth. Roll out 1 puff pastry sheet into a 12-inch square; cut into four 6-inch squares. Brush with egg wash and sprinkle with sugar. Spoon the cream cheese filling onto the squares and fold the corners into the centers until touching. Bake seam-side up at 400 degrees F until the pastry is golden, about 20 minutes.
