To make homemade apple crisp, peel, core and cut 5 pounds of McIntosh apples into large slices. Mix the apples with the grated zest from a lemon and an orange, 1/2 cup sugar, 2 teaspoons ground cinnamon, 1 teaspoon ground nutmeg, and 2 tablespoons each of lemon and orange juice.
Preheat the oven to 350 degrees Fahrenheit. Combine 1 1/2 cups flour, 3/4 cup granulated sugar, 3/4 cup light brown sugar, 1/2 teaspoon kosher salt, 1 cup oatmeal and 1/2 pound cold unsalted butter (previously diced) in the bowl of an electric mixer. Use the paddle attachment to mix on low speed until the butter pieces are the same size as peas, and the rest of the mixture has a crumbly texture. Scatter this evenly on top of the apples.
Place the baking dish on a sheet pan, and bake the crisp for about one hour. When the apples are bubbling and the top is brown, take the dish out of the oven. Serve while still warm, with a scoop of vanilla ice cream if desired. Prep time should take about 20 minutes, so the dish takes a total of 80 minutes to prepare. This recipe is designed to yield up to 10 servings.