• Preheat your oven to 375°F (190°C). Lightly grease an 8x8-inch baking dish.

For the berry layer

• In a large bowl, combine: 4 cups mixed berries, 2 tablespoon maple syrup, 1 tablespoon lemon juice, and 1 teaspoon vanilla extract. Stir together. Then add 1 tablespoon cornstarch, ½ teaspoon ground cinnamon, and ⅛ teaspoon salt. Stir together again.
  

For the crumble layer

• To a food processor add: 1 cup rolled oats, ⅓ cup nut butter, 3 tablespoon maple syrup, ½ teaspoon ground cinnamon, ¼ teaspoon ground nutmeg, and ⅛ teaspoon salt. Pulse the mixture 6–10 short pulses until it becomes crumbly and forms soft clumps when squeezed.
  
• You’re looking for a texture like: coarse crumbs with some larger pieces — not powder. If the mixture looks too dry or sandy, add: 1 tablespoon maple syrup or nut butter. Then pulse once or twice more.

  Sprinkle the crumble evenly over the berry mixture. Don't press it down.
• Transfer the berry mixture to the prepared baking dish and spread into an even layer.
  
• Bake at 375°F for 35–40 minutes, until the berries are bubbling and the topping looks lightly golden. Allow the crumble to rest for 10 minutes before serving so the filling can thicken.