method
1. Place the onions and potato slices in boiling salted water, cook until just tender and strain well.
2. In the meantime, to make the sauce, heat the margarine in a saucepan, stir in the flour and cook for several minutes.
3. Gradually pour in the milk, stirring, bring to the boil and cook, stirring, until thick and smooth.
4. Add salt and pepper to taste.
5. Arrange the onions and potatoes in layers in an ovenproof dish and pour over the sauce.
6. Sprinkle grated cheese on top and place under a hot grill until crisp and golden brown.
serving amount
serves 4
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