Chop the rhubarb into inch-long pieces, and the strawberries into quarters. Mix them together in a big bowl with the sugar, flour and add the lemon juice.
Split your pastry into two and roll out to fit a 9inch pie dish. After lining your pie dish with the first half of the pastry, spoon in the filling.
Moisten the edge of the bottom crust before you cover it with the top crust. Trim off the excess around the edge and pinch the two edges together.
Sprinkle the top of the pie with sugar and cut four little steam vents in the middle.
Bake in the bottom of the oven for 15 minutes at 220 degrees, then reduce the heat to 180 degrees and bake for a further 35 to 45 minutes.
Once out of the oven let it sit until it's cool enough to eat.
Personally I love pie with fresh pouring cream, but ice cream or fresh whipped cream is pretty amazing too. Pies are my favourite desert, well they're tied with baked peaches and ice cream if I'm being very honest, but if I had to live on a deserted island for a year I would ask for a supply of pie and the full works of Jane Austen to keep me company.