1. First, peel and slice the potatoes.

2. Skin the onions and also cut into even slices.

3. Put a layer of potato slices in a saucepan or roasting dish, then spread out a layer of onion slices.

4. Provide with knobs of butter and plenty of salt and pepper.

5. Then add another layer of potatoes, onions, butter, salt and pepper.

6. Continue until all the vegetables are used up.

7. The last layer should be potatoes.

8. Now pour over enough water and a dash of apple cider vinegar to just cover the potatoes.

9. Cook the onion potatoes for about 3/4 hour with the lid open until the sauce is slightly creamy.

Tip: Onions are easier to skin if you scald them in boiling water and let them sit until cool.