To make the pastry, put the flour, sugar, salt and ground ginger in a bowl and mix together before adding the butter. Using your fingertips, break down the butter into chunks, as though you were making shortcrust pastry. Don’t rub in the butter too fine, you want the mix to be textured - some bits of butter rubbed in finely with other larger pea sized pieces. Once roughly combined, stir through the buttermilk or homemade buttermilk with a knife and bring together with your hands, adding a little flour if it feels too sticky. Wrap in clingfilm and place in the fridge to rest for at least one hour.
To make the crumble, place the oats, sugar, flour and ginger into a bowl, mix briefly then add the butter. Rub the fat between your fingers to break down the butter until the mix resembles breadcrumbs. Set aside.
To prepare the filling, wash, top and tail the rhubarb stalks and slice into 1cm pieces. Add to a large bowl and then wash the cherries, removing the stones and stalks and cutting each one in half. Add to the bowl along with the sugars, cornflour and lemon juice and stir. Leave to macerate at room temperature.
Once you are ready to make the pie, dust a clean work surface with flour and roll the pastry into a large circle slightly bigger than your pie tin. I used a 23cm tart tin. Once rolled, carefully lift the pastry into the tin and press down lightly into the corners. Fold the edges outward but inside the tin to create a rounded top, cutting off pieces and sticking them in patchy parts. The pie dough is pretty forgiving, so it's good for patching any broken sides or cracks. Once happy, cover with clingfilm and place the pie in the fridge for at least 30 minutes.
Preheat the oven to 200oc/180oc fan and remove the pie case from the fridge, removing the clingfilm.
Add a handful of the crumble to the fruit and stir to soak up any juices then scoop the fruit into the pie case, levelling with a spoon or spatula. Sprinkle over the remaining crumble, covering all of the fruit and place the tin on a tray. Put the pie in the oven on the middle shelf and bake for 20 minutes, reducing the heat to 180oc/160oc fan for a further 45 minutes. Keep checking that the top isn't browning too quickly (cover with tin foil if it is) and bake until the fruit is tender. Once baked, remove from the oven and leave to cool on the tray and in the tin for to to three hours to let the juices settle. Serve with ice cream for pudding or for breakfast with a mug of black coffee.
Recipe by Victoria Sponge Pease Pudding at http://victoriaspongepeasepudding.com/baking/rhubarb-cherry-ginger-crumble-pie/