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For the pastry, put the flour in a mixing bowl and add the butter.
Rub the butter into the flour with your fingers until it resembles breadcrumbs.
Add the water to make a soft dough.
Refrigerate the pastry for 30 minutes, then roll it out to a size big enough to cover the top of your pie dish.
For the filling, put the vegetables, vegetable extract and rolled oats in a saucepan, add an inch or so of water and stir to avoid sticking. Cook for 10 minutes. Once cooled, transfer the mixture to a pie dish.
Cover with pastry and bake at 180°C for 40 minutes, or until the top is browned.