In a medium bowl, whisk the flour, granulated sugar and salt.
Using an electric mixer, beat 8 oz. cream cheese and the butter on medium-high speed until fluffy, 1 minute. Beat in the flour mixture on low speed. Divide the dough in half; place each half on a large piece of plastic wrap. Using the wrap to help, form the dough into disks and seal. Chill the dough until firm, at least 1 hour.
Meanwhile, in a small bowl, mix half the beaten egg into the remaining 4 oz. cream cheese. Stir 1 tsp. water into the remaining egg. Chill both the cream cheese mixture and the egg wash.
Position racks in the upper and lower thirds of the oven; preheat to 350 degrees. Line 2 cookie sheets with parchment. Working on a floured surface, roll out 1 disk of dough 1/4 inch thick. Using a 4-inch round cutter, cut out the cookies and place on the pans. Repeat with the remaining dough disk. Reroll any scraps and cut out enough cookies to total 24.
Transfer 1 of the pans to the refrigerator. Working with the other pan, place 1 tsp. of the cream cheese mixture and 1 tsp. jam in the center of each cookie. Using a pastry brush, coat the cookie edges with the egg wash; fold over the filling. Using the back of a fork, seal the edges. Brush the tops with egg wash. Place the pan in the refrigerator; repeat with the remaining cookies.
Bake the cookies until golden, 16 to 18 minutes. Transfer to a rack; let cool.
In a medium bowl, whisk the confectioners sugar with 2 tbsp. water. Working over the parchment, drizzle the cookies with the glaze. Sprinkle with the sparkling sugar. Let the glaze set.