For the pastry, put the flour, salt and butter in a bowl and rub in the butter until you have breadcrumbs. Add the vanilla extract and then the water, a tablespoon at a time, combining the mix with a knife or spoon, bringing it together until the mixture starts to clump together into a dough. You need to be cautious at this stage as you don’t want sticky pastry. Add a little more water if necessary, you want a smooth, solid ball of dough. Divide the lump into two and then flatten both into disc shapes, wrap in cling film and refrigerate for at least 30 minutes.
Preheat the oven to 200C/400F/Gas 6 and grease the pie dish. Remove a disc of pastry from the fridge, unwrap it and roll it out on a generously floured work surface to 3mm/¼in thick and about 2½cm/1in wider than the pie dish. Transfer to a floured baking sheet and chill for about 10 minutes. Repeat this process with the remaining disc of pastry.
Heat the jam for the filling in a saucepan with 100ml (3½ fl oz) water, nutmeg, bay and the vanilla extract. When it’s all melted together, add the diluted corn flour and stir together until smooth and thickened. Add the cherries and gently coat them in the mixture, being careful not to mush them up, so you preserve their shape. Remove from the heat and set aside.
Using a floured rolling pin, carefully transfer one of the chilled pastry sheets to the greased pie dish and drape it across the dish. Let it sink into the dish and, holding on to the edges, lift and tuck the pastry into the edges of the dish, all the way around, to line it. Trim off any excess pastry and lightly prick the base with a fork. Fill the dish with the cherry filling (including the bay leaf). Use a pastry cutter to cut holes in the remaining pastry sheet, covering an area just smaller than the diameter of the pie dish, leaving a large border intact. Place it over the pie filling and fold the edge of the top crust over the edge of the bottom crust, crimping it together with your fingers to seal.
Brush the pastry with the beaten egg and sprinkle over the granulated sugar. Bake for 20 minutes, until the crust is golden, then reduce the oven temperature to 180C/350F/Gas 4, covering the top of the pastry with foil if you need to, to avoid it burning, and bake for a further 30 more minutes, until the filling is bubbling and the pastry is golden, firm and lightly puffed.
Allow the pie to cool for about one hour before serving with cream.