Position a rack in the center of the oven and preheat to 350ºF.
In a large bowl, toss the apple wedges with the lemon, whiskey, sugar, cornstarch, and salt. Place the apples in an 8-inch round baking dish, pie plate, or ovenproof skillet (or a 9 by 7-inch oval baking dish, or another baking dish that the apples fill). Place the baking dish on a rimmed baking sheet to catch any drips, and bake until the apples are juicy, 20-25 minutes. Gently stir the apples to redistribute.
To make the topping, combine the almond flour, oats, nuts, oat flour, tapioca flour, brown sugar, cinnamon, nutmeg, and salt in a medium bowl (you can reuse the apple bowl if you scraped it clean enough). Stir in the melted butter until the mixture forms large clumps.
When the apples have baked, sprinkle the topping over the fruit. Return to the oven and bake until deep golden and bubbling furiously, 20-30 more minutes. Let cool for a few minutes or to room temperature, then spoon into bowls and serve with ice cream and a drizzle of butterscotch sauce, if using.
The crisp is best when freshly baked but leftovers keep, covered and chilled, for up to 3 days. Enjoy cold or warm.
Mix it up by using peaches, nectarines, cherries, or berries in the summer, or try other fall fruits such as pears, cranberries, persimmons, or quince, all sweetened to your taste.Try the hazelnut variation.For nut allergies, try using finely ground sunflower seeds in place of the almond flour and pumpkin seeds in the topping.To serve a crowd, double this recipe and bake it in a 10-inch skillet, or triple it and bake it in a 9 by 13-inch baking dish, increasing the bake time as needed for the fruit and filling.Nutritional values are based on one of four servings.