I got this recipe here but in case the other site ever goes down or something, I'm copying the recipe over as well. ☺
This recipe is fairly time consuming, but if you try it I think you'll agree that it's worth the effort. (Unfortunately it's not a terribly photogenic pie...it's soft and tends to slide and 'melt' a little even when properly chilled...but it tastes fantastic!)
1 baked and cooled 9" pie shell (it really will overflow an 8", so get yourself a nice big deep pan for this one!)
1 can blueberries in heavy syrup (15 oz), drained, reserving juice in one bowl and berries in another (if you use fresh berries, use around 2cups, and cook them down over low heat with a little water and around 1/2 c sugar until they thicken.)
1 1/2 c water (I found that this made the pie a little runny, so in the future I'll either reduce it or drain off half of it after the apples cook)
1 c pea-sized diced apple
3 Tbs cornstarch (you can substitute with 6Tbs flour, but you'll want a little extra water to blend it with, so you'll need to reduce the water elsewhere to balance it)
1/4 c water
3/4 c sugar
1/2 tsp lemon juice
1/4 tsp cinnamon
Sour Cream Topping
1 c sour cream
1 tsp vanilla
1/2 c sugar
1 Tbs cream cheese
1/2 tsp knox gelatin
2 Tbs cold water
In a medium saucepan combine diced apples with 1 1/2 c water and sugar at medium temperature until the apples are done but not mushy. (Do make sure they are done, otherwise the texture will stand out from the blueberries...it tastes fine, but the texture of a not-quite-cooked apple is a little odd in the middle of a blueberry pie!)
While the apples are cooking mix cornstarch with 1/4 c water until dissolved. When apples are done add lemon juice and berry juice, cook and stir until blended. While stirring on medium heat add dissolved cornstarch slowly and stir constantly until thickened. Add berries and cinnamon and mix well. Remove from heat and cool before placing into cooled prepared pie shell.
Refrigerate until thoroughly chilled.
Dissolve gelatin in 2 Tbs water and set aside. Mix the sour cream, sugar, and cream cheese in a pan on low heat until sugar is dissolved and everything is mixed thoroughly. Stir and watch that mixture does not burn or dry out. When all is smooth and blended add vanilla and stir. Then gradually add gelatin until mixture has a firm consistency of soft pudding. Remove from heat.
Topping can be smoothed over blueberries while luke warm, then chill the whole pie.
*If you are on a tight schedule you may substitute blueberry pie filling, but it will be sweeter... if you do this, it replaces the entire filling mixture--not just the blueberries. When I tried this though it did not set up very well. The pie tasted great, but it was very runny.