Basically, make a jam from your blueberries, but not too mushy since they cook quickly. Add sweetener as needed, enough to make it a little syrupy, but not so much that they get too sweet. Both vanilla and lemon juice are nice flavors for blueberries, so those go in, as well.
We're transitioning off of GAPS at the moment, so I did make a base of arrowroot starch and water to start.
Make a top and bottom crust of your choice (Fife uses a nut topping, but that's not a possibility for us, so we went with a regular crust).
It was super-yummy topped with unsweetened yogurt.
Here it is (I have, as yet, to be able to get photos of any pie that hits our table before it gets eaten!).