WHY THIS RECIPE WORKS: Making an apple crumble that tastes primarily of apples starts with plenty of fruit. We tossed 4 pounds of apples with 2 tablespoons of lemon juice to enhance their bright flavor. Adding just 2 tablespoons of brown sugar to the filling kept the apples from tasting too sweet. We baked the apples in a covered pan before applying the topping, which allowed them to collapse into a thick layer of filling. Adding nuts to the streusel loosened its consistency so that it didn’t bake up dense, and a couple of teaspoons of water hydrated the flour so that the mixture clumped nicely. Applying the topping midway through baking minimized its exposure to the juicy fruit, preventing it from becoming soggy.