Heat the Oven - Set the oven rack to the center position. Heat to 375ºF (191ºC).
Prepare the Apples - Peel, core, and cut the apples into ½-inch thick slices.
Make the Filling - In a large bowl, stir to combine sliced apples, granulated sugar, brown sugar, cinnamon, nutmeg, salt, lemon zest, and lemon juice.
Cook the Apple Filling - Heat a large skillet over medium heat. Once hot, add the butter and the apple mixture. Saute until crisp-tender, and most of the moisture is released, about 15 to 20 minutes.
Prepare the Baking Dish - Lightly butter the bottom and sides of an 8 by 8-inch baking dish. Evenly spread the cooked apples inside the dish.
Crisp Topping
Mix the Dry Ingredients - In a medium bowl, whisk together the flour, rolled oats, brown sugar, cinnamon, salt, and nutmeg.
Make the Topping - Cut cold butter into ¼-inch cubes and add to the flour mixture. Use fingers to break the butter into the dry ingredients, pressing together to create large pebble-shaped pieces of crumbly topping, about the size of a dime. Evenly sprinkle the topping over the apples.
Bake the Crisp - Bake until the topping is golden brown and crisp, about 30 to 35 minutes. Transfer to a wire rack and cool for 10 to 15 minutes.
To Serve - Serve warm with desired toppings.
Notes
Apple Substitutes: Gala or McIntosh apples have a taste similar to Honeycrisp. Use Granny Smith apples for a more tart flavor.
Make it in a Skillet: Bake inside an 8 to 10-inch cast iron pan.
Make it Gluten-Free: Substitute gluten-free rolled oats and gluten-free flour.
Make it Dairy-Free: Substitute coconut oil instead of butter.
Storing: Cool completely then cover with foil or transfer to an airtight container. Refrigerate for up to 5 days.
Reheating: Heat individual portions in the microwave in 15 to 30-second intervals until warm. You can bake the whole dish at 350ºF (177ºC) until the top is crisp and the filling is warm.