Preheat the oven to 180ºC/gas 4. Trim and finely slice the leeks, then sautée with a splash of oil until soft and sticky. Chop the bacon, then fry in a separate pan until golden. Coarsely grate the cheese. Whisk together the eggs, then stir through the cheese, milk, leeks, bacon and a good pinch of seasoning. Place the pastry case onto a baking sheet, then pour the mixture into the case and bake for 25 to 30 minutes, or until golden. Delicious served with a mixed green salad.