If you don’t have a rectangular tin, don’t let that put you off — a round one will do fine. The key to this simple tart is cooking the leeks long and slow to ensure they are really soft. No one likes chewy leeks.
- For the pastry, place the flour, salt and butter into a kitchen processor, blitzing until it resembles fine breadcrumbs. Add the egg and 1 tablespoon cold water and blitz to form the dough. Add a little extra water if needed. Roll the pastry on a lightly floured bench to fit a 12 x 35cm tin. Refrigerate for 20 minutes.
- Preheat an oven to 180. Bake the pastry blind for 20 minutes. Remove.
- Heat the butter and oil in a large pot. Add the leeks and garlic, cooking slowly for about 10 minutes until completely softened. Remove and place into the tart case. Dot with the salmon and sprinkle with the cheese.
- Combine the milk with the eggs and thyme, season well then pour carefully over the filling. Place back into the oven for 40 minutes until the centre has set. Remove and cool for 10 minutes before serving.