11-1/4 oz. (2-1/2 cups) unbleached all-purpose flour
2 Tbs. granulated sugar
1/2 tsp. kosher salt
6 oz. (3/4 cup) cold unsalted butter, cut into 12 pieces
6 oz. cold cream cheese, cut into 6 pieces
1/2 cup heavy cream
3 oz. cream cheese, softened
7 Tbs. granulated sugar
Seeds scraped from 1/2 vanilla bean (or 1/2 tsp. pure vanilla extract)
1 large egg yolk
1 cup blueberries
2 tsp. cornstarch
1/8 tsp. kosher salt
1 large egg yolk
Make the dough:
Put the flour, sugar, and salt in a food processor. Add the butter and cream cheese and pulse until the mixture resembles coarse meal, 8 to 10 pulses. Add the cream and pulse, pausing to scrape the bowl once or twice, just until the dough starts to come together, 8 to 10 pulses more. Do not overprocess. Turn the dough out onto a clean work surface, gather it together, and pat it into a rectangle. Wrap it in plastic and refrigerate for at least 2 hours and up to 3 days.
In a medium bowl, combine the cream cheese, 3 Tbs. of the sugar, the vanilla bean seeds (or extract), and 1 egg yolk. Mix with a wooden spoon until well combined and smooth.
Combine the blueberries, 2 Tbs. of the sugar, the cornstarch, and salt in another medium bowl and mix gently.
Assemble and bake the turnovers:
Position racks in the top and bottom thirds of the oven and heat the oven to 400°F. Line 2 large rimmed baking sheets with parchment.
On a lightly floured surface with a lightly floured rolling pin, roll the dough into a 13x18-inch rectangle. Be sure to loosen the dough several times and re-flour underneath so it doesn’t stick. Trim the edges straight to form a 12x16-inch rectangle and cut the dough into twelve 4-inch squares. Put six squares on each baking sheet.
In a small bowl, beat the egg yolk with 1 tsp. water. Brush the outer edges of each dough square with egg wash. Dollop 1/2 Tbs. of the cream cheese mixture in the center of each round. Top with 1 Tbs. of the blueberry mixture. Fold in half to form a triangle shape and pinch the edges together to seal them. Lightly brush each pie with egg wash and sprinkle with 1/2 tsp. of the remaining sugar. With the tip of a paring knife, cut a steam vent in the center of each pie.
Bake until the turnovers are browned and the filling is bubbling, 25 to 30 minutes, swapping and rotating the baking sheets’ positions about halfway through baking. (Don’t worry if juice leaks out.)
Transfer the baking sheets to racks and allow to cool for 5 minutes. Then loosen the turnovers with an offset spatula and cool completely on the sheets. The turnovers are best the day they’re made.