Preheat the oven to 350°F (180°C) and grease a 9x9-inch baking dish with non-stick cooking spray or softened butter. Set it aside.

In a large bowl, combine the chopped apples, brown sugar, 1/4 cup of all-purpose flour, 2 tsp of ground cinnamon, and 1/4 tsp of ground nutmeg. Toss the mixture until the apples are coated evenly with the sugar and spices. Then, transfer the apple mixture into the prepared baking dish and spread it evenly.

In a separate mixing bowl, make the topping. Combine the old-fashioned oats, 1/4 cup of all-purpose flour, 1/2 cup of brown sugar, cold diced butter, 1 tsp of ground cinnamon, 1/4 tsp of ground nutmeg, and a pinch of kosher salt. Use a fork or a pastry cutter to mix the ingredients until the mixture resembles coarse crumbs and the butter is evenly distributed.

Sprinkle the topping mixture evenly over the apple filling in the baking dish, covering it completely. Use a silicone spatula or the back of a spoon to gently press down on the topping to even it out.

Place the baking dish in the preheated oven and bake for about 40-45 minutes or until the top is golden brown and the filling is bubbly around the edges.

Once done, remove the apple crisp from the oven and let it cool slightly before serving. You can enjoy it on its own or with a scoop of vanilla ice cream.

Serve warm and enjoy your delicious homemade apple crisp!