To make apple crisp topping, combine 1/2 cup of brown sugar with 1/2 cup of dry oatmeal, 1/3 cup of flour and a pinch of salt. Cut 1/4 cup of cold butter into small pieces, and blend them into the dry ingredients with your hands until nickel-sized clumps form.
For a richer topping, increase the amount of butter to 6 tablespoons, and use 3/4 cup of sugar. Boost the flavor by stirring 1/2 teaspoon each of cinnamon and nutmeg into the mix of dry ingredients. If you don't want to get your hands dirty, combine the butter and dry ingredients using a stand mixer on a low setting. Stop the mixer when the topping forms pea-sized clumps.
Create a heartier topping by stirring in 1/4 cup of chopped walnuts or pecans before or after adding the butter. Chop the nuts roughly for a crunchier topping, or use a fine chop for a more subtle effect.
Adjust the topping recipe to suit your tastes. Use white sugar for extra sweetness, or add a deep toffee flavor by switching the brown sugar with raw turbinado sugar. Stir in a tablespoon of fresh lemon zest to give the topping a lighter, fruitier taste. If your topping tastes too sweet, add an extra pinch of salt.