Instructions

1. Form the tart shells:
2. Lightly dust a work surface with all-purpose flour. Place 1 pie dough on the work surface and roll out until about 1/8-inch-thick. Cut out 12 rounds with a 3-inch round cookie cutter. Gather the scraps together, shape into a ball, and refrigerate.
3. Press each round into a well of a mini muffin tin, pressing in the center and working your way up the sides to form a crust in each one. The dough should hang slightly over the edge.
4. Re-roll the remaining dough. Cut out 6 more rounds (discard any remaining dough) and line 6 more mini muffin wells. Refrigerate while you make the apple filling.
5. Make the apple filling:
6. Heat the oven to 375ºF.
7. Melt 2 tablespoons unsalted butter in a medium saucepan over medium heat. Stir in 1/4 cup packed dark brown sugar, 1 1/2 teaspoons apple pie spice, 1/4 cup of the water, 1 teaspoon lemon juice, 1 teaspoon vanilla extract, and 1 pinch kosher salt. Cook, stirring continuously, until the brown sugar is dissolved, about 30 seconds.
8. Stir in 2 3/4 cups finely diced apples. Cook, stirring frequently, until the apples are slightly softened but still have a slight bite to them, about 15 minutes. Meanwhile, whisk the remaining 2 tablespoons water and 2 teaspoons cornstarch together in a small bowl until the cornstarch is suspended.
9. Give the cornstarch mixture another whisk, then pour into the apple mixture. Cook, stirring often, until the filling is glossy and thickened, about 1 minute more.
10. Remove the saucepan from the heat. Let cool until just warm to the touch, 10 to 15 minutes.
11. Assemble and bake:
12. Divide the apple filling between the tart shells (about 1 heaping tablespoon per shell).
13. Bake, rotating the mini muffin tin(s) halfway through, until the crust is a deep golden brown and the apple filling is bubbly, about 25 minutes total.
14. Let the apple tarts cool in the pan for 5 minutes. Transfer the tarts to a wire rack. Serve warm or let cool completely.