Toss blueberries with 1/3 cup sugar, lemon juice, cornstarch and salt in a bowl. Whisk cream cheese, egg yolk 2 T sugar and nutmeg in another bowl.
Spread half of the cream cheese mixture over dough leaving a 2 inch border. Top with blueberries. Drizzle the remaining cream cheese mixture over the berries. Fold the edge of the dough over the filling, pleating it every few inches.
Brush egg over dough and sprinkle with sugar. Bake in the lower 1/3 of oven at 425 until golden, 20-25 minutes