Preparation

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.

  When ready to bake, position racks in the bottom and top 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 13×18-inch rectangle. Be sure to loosen the dough several times and reflour underneath so it doesn’t stick. Trim the edges straight to form a 12×16-inch rectangle and cut the dough into twelve 4-inch squares. Put six squares on each baking sheet.

Make the filling

• In a medium bowl, lightly toss the blackberries, apple, brown sugar, flour, allspice, and salt until combined.

Assemble and bake the turnovers

• In a small bowl, beat the egg yolk with 1 tsp. water. Brush the outer edges of each dough square with egg wash. Spoon 2 rounded Tbs. of the filling into the center of each square. Bring the points together into a triangular shape, pressing to seal the edges. Lightly brush the top of each turnover with egg wash and sprinkle with a scant 1/2 tsp. granulated sugar. With the tip of a paring knife, cut a steam vent in the center of the top crust of each turnover.

  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.