Step 1

Heat the oven to 375°F and lightly grease a 9x13-inch baking dish with baking spray.

Step 2

Toss the blackberries and rhubarb together gently with the brown sugar, cinnamon, ginger, and salt. Spread in the prepared baking dish.

Step 3

In a medium bowl, whisk the flour with the baking powder and salt. Whisk in the brown sugar, breaking up any large clumps. In a small separate bowl, whisk the eggs with the vanilla. Pour the egg mixture into the flour mixture and use your hands to mix the eggs into the flour. Squeeze and pinch the mixture together; it will be clumpy, with a loose scree of crumbs at the bottom of the bowl.

Step 4

Drop the larger, wetter clumps of dough over the fruit. Shake the drier crumbs over top, distributing the douhg evenly over the fruit. Sprinkle the top with the chopped walnuts, then pour the melted butter over everything.

Step 5

Bake for 35 minutes, or until the top is golden brown and the crumble is baked through. Let sit for about 30 minutes before eating.