For 4 people you need

2 good sized onions 4 large potatoes seasoning

For the sauce

1 oz. margarine 1 oz. flour 1/2 pint milk seasoning. 2-3 oz. grated Cheddar cheese

Peel both the onions and potatoes.
Slice onions thinly, and potatoes thickly, and cook in boiling salted water until just tender, then strain.
Meanwhile make the sauce: Heat the margarine in a pan,stir in the flour and cook for several minutes, then gradually stir in the milk, bring to the boil and cook stirring well until thickened and smooth, season.
Arrange vegetables in a dish with the sauce, top with grated cheese and cook under grill until crisp and brown.