Heat the oven and prep the dish. Preheat to 350°F (175°C). Lightly butter or spray a 9x13-inch baking dish or similar.

Prep the apples. Peel, core, and slice the apples about 1/4-inch thick. Keep the slices even so they cook at the same rate.

Toss the filling. In a large bowl, combine apples with lemon juice, granulated sugar, 2 tablespoons flour, 1 teaspoon cinnamon, a pinch of salt, and vanilla if using. Add raisins or dried cranberries if you like. Toss until the apples look lightly coated.

Make the crisp topping. In another bowl, combine the remaining flour (about 1/2 cup plus 2 tablespoons), rolled oats, brown sugar, 1 teaspoon cinnamon, nutmeg if using, and 1/4 teaspoon salt. Add the cold butter cubes and cut them in with a pastry cutter or your fingers until the mixture looks like coarse crumbs with pea-sized bits of butter. Stir in nuts if using.

Assemble. Spread the apple mixture evenly in the baking dish. Scatter the topping over the apples, covering them as evenly as possible without packing it down.

Bake. Bake for 40–50 minutes, until the topping is golden brown and the apples are bubbling around the edges. If the top is browning too fast, tent the dish loosely with foil for the last 10 minutes.

Rest and serve. Let it sit for at least 10–15 minutes so the juices thicken. Serve warm on its own or with vanilla ice cream, whipped cream, or a drizzle of heavy cream.