Ingredients

For the Apple Filling:
Soft butter for greasing casserole dish
8 to 9 cups peeled, cored and sliced apples (about 7 to 8 large apples)
3 tablespoons sugar
1 tablespoon lemon juice

For the Oatmeal Topping:
1 cup flour
1/2 cup old-fashioned rolled oats
1/3 cup sugar
1/3 cup packed light brown sugar
1/2 teaspoon cinnamon
1/2 cup cold, unsalted butter, cut into 1/4-inch pieces
1/2 cup chopped pecans or walnuts (optional)

Heat the oven to 375 F. Generously grease a shallow, 13-by-9-inch casserole with soft butter. Pile the sliced apples in the casserole. Sprinkle the sugar and lemon juice over them and stir the fruit gently, right in the pan. Once the slices are evenly coated, spread them uniformly.
Combine the flour, oats, sugar, brown sugar, cinnamon and salt in a large mixing bowl. Toss the ingredients with your hands to mix them. Add the unsalted butter pieces to the dry ingredients and use your fingers to rub in the butter until you have pea-size crumbs. At this point, none of the flour should be noticeable. Mix in the pecans or walnuts, if desired.
Spread the topping evenly over the apples and press it down gently with your palm. Bake the crisp on the center oven rack for 45 to 50 minutes, until juice bubbles around the edges and the topping is golden brown. If the top starts to get too brown, move the crisp down one shelf.
Transfer the crisp to a wire rack and cool for at least 15 minutes before serving. Makes 9 to 12 servings.

Vanilla Custard Sauce

6 large egg yolks
1/2 cup sugar
2 cups light cream
2 teaspoons vanilla extract

Directions

Whisk together the yolks and sugar in a mixing bowl. Bring the cream just to a simmer in a medium-size nonstick saucepan and promptly remove it from the heat. Stir the hot cream into the yolks, adding about 1/3 cup at a time. Pour the mixture back into the saucepan.

Cook the custard over medium-low heat without letting it boil, stirring continuously, until it thickens to the consistency of heavy cream (about 7 minutes). Watch the sauce carefully, because the change is subtle.

Strain the sauce through a fine-mesh strainer into a small bowl. Stir in the vanilla extract. Let the sauce cool to room temperature, then chill it, covered, until cold. It will keep for 2 to 3 days. Whisk it briefly just before drizzling it on the crisp. Makes about 2 1/2 cups.