Rhubarb has a high water content and exudes considerable juice as it cooks. To help prevent the juice overflowing, toss the cut rhubarb in a little flour before putting it into the pie dish: the flour will thicken the juice as the pie cooks and help to keep it contained. Use a level tablespoon of plain flour to each 500 g of prepared fruit, and mix it with the sugar before tossing with the rhubarb.
Also, when making the pie, ensure that the pastry edges are well sealed. Make a small hole in the top of the pie to let the steam escape as this will prevent the steam forcing the sealed edges apart and will allow some of the juice to evaporate. As a final precaution, always stand the pie dish on a baking tray to catch any juice that could overflow and burn on the bottom of the oven.
** Asian Recipes