How to Make It
Preheat oven to 375°F with rack in lower third of oven. Line bottom of oven with aluminum foil or an oven liner. Lightly coat a standard 12-cup muffin tin with non-stick spray.
Working with 1 piecrust at a time, on a lightly floured surface, roll each out to a 12-inch diameter. Cut 2 6-inch rounds and 2 3½-inch rounds from each piecrust. Cover and chill the smaller rounds until ready to use.
Fit a 6-inch round into each cup of prepared tin, pressing and flattening into the sides of muffin cups and leaving about ½-inch overhang. Chill until ready to use.
Combine butterscotch chips, 3 tablespoons of the heavy cream, and ¼ teaspoon salt in a microwave-safe bowl. Microwave on HIGH, stirring every 30 second, until melted and smooth, about 1 minute and 30 seconds. Set aside.
Stir together apples, sugar, butter, cornstarch, lemon juice, cinnamon, and remaining ¼ salt in a large bowl. Spoon about ½ cup apple mixture into each prepared crust; drizzle butterscotch sauce over apples (about 1 tablespoon per pie).
Top each mini pie with 1 smaller piecrust round. Fold overhang from bottom crust over top crust, and crimp to seal. Cut an “X” in middle of top crust and brush with remaining 2 tablespoons heavy cream.
Bake on lower rack until crust is golden and filling is bubbly, 40 to 45 minutes, tenting with foil after 30 minutes if pies are browning too deeply. Remove from oven, and cool in pan 5 minutes. Gently remove pies from muffin tin and transfer to a wire rack. Let cool completely, about 1 hour.