I am a rhubarb hoarder. There’s always a surplus of it from the allotment and I make sure that I chop some up to be frozen. If you treat it well, rhubarb is amazing for making pies. It naturally contains quite a lot of liquid and has a pretty tart flavour, though, meaning you need something to absorb the excess liquid (hopefully not the pastry underneath) and something to sweeten it. I mix some of the crumble mixture into the filling for this purpose, and this has bonus points (!) because it also makes the filling buttery and gooey. It’s just perfect. As well as fresh blueberries I have added dried blueberries to the mixture, which absorb some of the liquid as the pie bakes, plumping them back up.