This is my mum's recipe. I cheat, however, and use shop-bought shortcrust pastry. You can also use this filling for rhubarb turnovers using puff pastry.
Don't bother with the butter; you don't need it at all. And do NOT--as some other reviewers have suggested--mix up the flour/sugar mixture with the fruit before adding the fruit to the case. The reason you want copious amounts of sugar both on the bottom and on the top of the fruit (rather than mixed amongst it) is that while baking, the bubbling-hot sugar carmelises in contact with the bottom and top pastry, a process which makes the pastry rather crispy in the final product. If you mix the sugar with the fruit, you don't get that crispy pastry, and the large amount of water in the rhubarb will definitely make the bottom crust sodden. Don't worry: the sugar makes its way through the fruit anyway, so you won't have parts too sweet and other parts too tart. - 21 Jul 2008
I liked this recipe. I tried it with only rhubarb and then the next time with strawberries and rhubarb. It was too sweet when I added strawberries and runny. I recommend using only rhubarb and not adding strawberries. With rhubarb, it was GREAT!!! - 21 Jul 2008
Excellent. Easy to prepare. However, I added a few strawberries (which I think improved) and I coated the pastry with a beaten egg (nicer color) - 20 Mar 2012