Harry and David's is the absolute best to use as a filling unless you make your own. I making your own.
Take blueberries and add a small amount of water, don;t add a bunch to drown them. Bring to a boil and let simmer until the berries burst and break down, add a slurry of cornstarch and water to thicken the sauce. Be sure the berries are at a brisk boil in order for the cornstarch to thicken correctly. Voila, blueberry filling. Let it cool and use as you would any other filling. If it is a little too tart then add a small amount of sugar and while you are cooking it put 1tsp of lemon juice to bring out the flavor of the berries.
I made this cake The other day, the filling was to die for. http://leitesculinaria.com/3041/recipes-marbled-lemon-blueberry-butter-cake.html
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