Rub the margarine into the flour with the salt until you have breadcrumbs. Add water a little at a time using a round-bladed knife to mix until the mixture just comes together. Form into a ball, cover with clingfilm and chill for 20-30 minutes. Preheat the oven to 180ºC/350ºF/gas mark 5 with a baking sheet in to heat up. Heat the butter in a pan and cook the onion until lightly gold and soft. Add the courgettes, aubergine and pepper and cook until tender - about 10-15 minutes. Set aside to cool. Roll out the chilled pastry and press it gently into a lightly greased flan tin. Prick all over with a fork and bake in the oven on the baking sheet for 20 minutes until pale gold. While the pastry case is cooking, whisk the eggs thoroughly, then whisk in the crème fraîche, milk, Parmesan and a little seasoning. Remove the pastry case from the oven, tip the cooked vegetables in then pour the egg mix over and bake for 35-40 minutes until the centre is set and the filling golden and puffy.