I have frozen blackberries in gallon bags of brie that i use, and i think you can buy blackberries at the grocery store
Put the berries on the stove with the water and sugar and cook until the juice is thick, taste test to see if you have enough sugar and set aside
°1 stick of butter
°1 and 1/2 cups of Bisquick
°1 cup of sugar, 1 cup of milk
* Methods :
Melt butter in baking dish, stir crackers, sugar, and milk into center of butter mixture, pour in blackberry juice, and bake all at 350° until golden brown or check done.