3 cups fresh blackberries or blueberries or raspberries
1⁄2 cup sugar
1⁄3 cup orange juice
4 teaspoons cornstarch
For the Blackberry Filling:
In saucepan, bring blackberries, sugar and orange juice to boil; reduce heat and simmer until tender, about 10 minutes.
Whisk in cornstarch and boil, stirring, until thickened, about 1 minute.
Place plastic wrap directly on surface; refrigerate until cooled, about 1 hour or up to 1 day before using.
For the Base and Crumble Topping:
In a large bowl, stir together the oats, flour, brown sugar, salt and baking soda. Cut in the butter to form a crumbly mixture. Reserve 1 1/2 cups of the crumbs, and pat the rest evenly into the bottom of a greased 9 x 13 inch pan.
Spread the blackberry mixture over the base. Crumble the reserved amount of the base/topping over the blueberry mixture.
Bake at 350 degrees F until light golden, about 40-45 minutes. Let cool completely on rack as these cut better when they are fully set.