Preparation In electric mixer, beat butter, cream cheese, and sugar at high speed until fluffy, about 5 minutes. Add egg yolks, vanilla, and salt and beat at medium speed until blended. Add flour and mix at low speed until just combined. Divide dough into thirds, form into 3 disks, and wrap in plastic wrap or waxed paper. Chill until firm, at least 1 hour or up to 2 days. Arrange racks in upper and lower thirds of oven and preheat to 375°F. Line 2 heavy large baking sheets with parchment paper. Beat together whole egg and milk to create egg glaze. Remove 1 dough disk from refrigerator. On well floured work surface, roll out dough to 1/8- to 1/16-inch thickness, dusting with more flour as necessary. Using 3- to 4-inch star cookie cutters, cut out cookies; transfer with spatula to baking sheets. Gather and reroll scraps and cut out additional cookies. Brush lightly with egg wash and sprinkle with sanding sugar. Bake cookies until golden and somewhat firm to touch, about 10 minutes. Cool on pans 2 minutes, then transfer to racks and cool completely. Repeat with remaining dough.
Preparation In electric mixer, beat butter, cream cheese, and sugar at high speed until fluffy, about 5 minutes. Add egg yolks, vanilla, and salt and beat at medium speed until blended. Add flour and mix at low speed until just combined. Divide dough into thirds, form into 3 disks, and wrap in plastic wrap or waxed paper. Chill until firm, at least 1 hour or up to 2 days. Arrange racks in upper and lower thirds of oven and preheat to 375°F. Line 2 heavy large baking sheets with parchment paper. Beat together whole egg and milk to create egg glaze. Remove 1 dough disk from refrigerator. On well floured work surface, roll out dough to 1/8- to 1/16-inch thickness, dusting with more flour as necessary. Using 3- to 4-inch star cookie cutters, cut out cookies; transfer with spatula to baking sheets. Gather and reroll scraps and cut out additional cookies. Brush lightly with egg wash and sprinkle with sanding sugar. Bake cookies until golden and somewhat firm to touch, about 10 minutes. Cool on pans 2 minutes, then transfer to racks and cool completely. Repeat with remaining dough.