Preheat your oven to 350 degrees.

In a medium bowl mix together blackberries, sugar and cornstarch.

Pour fruit into a sprayed 7x 10 or 8×8 baking dish.

In the same bowl, mix together flour, brown sugar, nuts, cinnamon, and salt.

Add in melted butter and mix with a fork. Mixture will be lumpy.

Sprinkle the clumped mixture over the fruit, leaving some of the clumps larger, so it stays crispier while baking.

Bake for 35-40 minutes, or until topping is lightly golden brown and fruit is bubbling.

Cool for about 15 minutes before serving. Serve with vanilla ice cream.