Whisk together together the water and cornstarch in a semi-large microwave-proof jug or dish. [Optional: a small splash of Kitchen Bouquet for a deeper colour.]
Open the jar of beef stew; pour liquid into a measuring cup. If you are short of 350 ml (1 ½ cups / 12 oz), then add some tap water, beer, wine or stock, etc, to top up.
Add this liquid to the cornstarch mixture. Whisk.
Zap in microwave for 1 minute.
Whisk, then zap in microwave for another 2 minutes. Remove, stir, set aside.
Start heating the oven to 175 C (350 F / Gas Mark 4.)
Mix together everything from the flour down to and including the baking powder.
Add the fat, and cut it in to the texture of coarse sand.
Add the liquid to bind the flour together to form a ball; add a bit more liquid if needed.
Divide the beef mixture between two small oven-safe casserole dishes that will hold about 1 cup (250 ml / 8 oz) each, or a bit more.
Divide the dough mixture into two balls, and roll out each one on a floured surface. Cut a few slits in each one, then use to cover the baking dishes with, pressing the sides down.
Brush with milk or spray with cooking spray if desired (optional, for a browner colour.)
Bake for 30 to 35 minutes or until crust is cooked and browned.
Remove from oven. Let cool 5 to 10 minutes before serving.