Combine the raisins and water in a saucepan. Bring to a boil and cook for 5 minutes to plump the raisins and build a flavourful liquid.
Thicken the filling
In a small bowl, whisk together the brown sugar, cornstarch, ground cinnamon, and salt. Stir into the hot raisin mixture. Cook over medium heat, stirring constantly, until the mixture thickens and the liquid turns clear -- about 7 to 8 minutes
Finish and Cool
Remove from heat. Stir in lemon juice, lemon zest, and unsalted butter. Let cool to room temperature before filling the crust. Do not skip this -- warm filling softens the pastry.
Assemble
Preheat oven to 220°C (425°F). Line a 9-inch pie plate with the bottom crust. Pour in the cooled filling. Cover with the top crust, seal and crimp the edges, and cut a few steam vents in the top. Brush the top crust with milk l sprinkle with sugar.
Bake
Place on the lower rack of the oven. Bake at 220°C (425°F) for 15 minutes, then reduce heat to 180°C (350°F) and bake for another 20 to 25 minutes until the crust is golden. Check at 15 minutes -- if the crust is already well browned, take it out rather than risk burning.
Notes
The vinegar version: Swap the lemon juice for 1.5 tbsp white vinegar for a sharper, more old-fashioned flavour.Orange juice version: Replace ½ cup of the water with orange juice and use orange zest instead of lemon.Serve with: Vanilla ice cream or sharp cheddar.My Granny's Pie Crust