1. Put the tomatoes into the pastry case.
2. Fry the onion in the butter and sprinkle over the tomatoes.
3. Beat the eggs, add the milk, seasoning and most of the cheese.
4. Pour into the pastry case and sprinkle with the remaining cheese.
5. Bake in a moderate oven (350°F - Gas Mark 4) until firm and lightly browned.