Grease an 8×8 pan (or double the recipe for a 9×13).

If using frozen berries, thaw first. Combine berries, sweetener of choice, and cornstarch, then spread into the pan.

Combine all remaining ingredients except butter in a mixing bowl.

Cut butter into the dry ingredients with a fork or pastry cutter until small crumbles form.

Sprinkle the crumbles evenly over the berries.

Bake on the center rack 25-30 minutes or until bubbly and lightly browned. Let cool before serving, as it thickens while it cools. The crumble will also thicken overnight.

Store leftovers covered in the fridge, or they can also be frozen.