Preheat oven to 350°F.

Make the crumble by combining the flour, brown sugar, oats, cinnamon and salt in a large bowl. Use a pastry blender to cut in the butter until the mixture forms small crumbs. You may need to use your hands to help it along. Set aside.

Place strawberries and blueberries in a large bowl. Toss gently with sugar, lemon juice, and cornstarch. Spread evenly in the bottom of an 8x8 inch baking pan.

Pour the crumble mixture over the berry filling and press down slightly to compact.

Bake for 30-33 minutes, or until the topping is golden brown and the filling is bubbly. Let cool slightly before serving warm with whipped cream or ice cream.