Cream Cheese Dough
1/2 lb. cream cheese
1/2 lb. butter
4 cups unbleached flour
4 to 6 tbsp. heavy cream or 2 egg yolks
1 tbsp. unsalted butter
1/4 cup plus 2 tbsp. sugar
1/2 tsp. fresh lemon juice
2 large Granny Smith or other tart, green apples, about ¼ lb., peeled and cut into ¾-inch cubes, about 3 cups
1 cup unfiltered apple juice
1/2 cup water
1 (2-inch) cinnamon stick
2 large quince, about ¾ lb., peeled, cored and cut into ¾-inch cubes, about 3 cups
2 1/2 tsp. tapioca starch
Egg wash, made by beating 1 large egg with 1 tsp. water
Cinnamon sugar, made by combining 1 tbsp. ground cinnamon with 1 cup sugar (see note)
Cream Cheese Dough
In the work bowl of a food processor, cream butter with cream cheese (1/2 at a time). Gradually add flour and mix with on/off pulse until mixture resembles fine cornmeal. Add just enough cream to make a ball, making sure not to over-beat. Form dough into a ball, wrap in plastic and refrigerate for 15 minutes.
Lightly flour a rolling pin and work surface. Roll dough into 6 (8-inch) rounds, about 1/4 inch thick. Stack dough rounds on a plate with a layer of parchment paper between each, cover with plastic wrap and refrigerate.
Melt butter in a medium-sized sauté pan, add 2 tbsp. sugar, salt and lemon juice; cook over medium heat until sugar is dissolved and bubbling, 2 to 3 minutes. Add apples and cook until just tender, about 5 minutes. Transfer to a medium-sized bowl and set aside to cool.
Combine apple juice, water, cinnamon stick and 1/4 cup sugar in a medium-sized saucepan and bring to a boil. Lower heat, add quince and simmer until tender, 5 to 6 minutes. Set aside to cool. Drain quince (saving the liquid if you like), add to apples and toss fruit with tapioca starch and additional sugar.
Preheat oven to 375 degrees and set oven rack to the middle position. Remove dough rounds from refrigerator.
Place 1/3 cup of the fruit in the center of each round and brush edges with egg wash. Fold dough over filling to form a half-moon. Seal and crimp edges with the back of a fork. Brush turnovers with egg wash and sprinkle lightly with cinnamon sugar. Place on a parchment-lined baking sheet and bake until golden, about 25 minutes.
Note: Any leftover cinnamon sugar is great to have on hand to sprinkle over pastries, cookies and toast. Store in an airtight container.