From the latest issue of Cooks Illustrated. The secret is using a grated apple to add extra pectin and get the filling to gel up nicely but still taste like fresh berries without turning it into glupe.  I think it worked, but we were supposed to wait 4 hours for the pie to cool properly, and we could only muster 45 minutes. So it was still warm and runny when we had our first piece, but this morning it looks legitimately sliceable.

There's also vodka in the crust which they didn't explain at all. Very mysterious and Russian.