1 - Melt the butter with the oil in a large heavy-based pan.

2 - Add the onions and fry with the lid on for 10 mins until soft.

3 - Sprinkle in the sugar and cook for 20 mins more, stirring frequently, until caramelised.

4 - The onions should be really golden, full of flavour and soft when pinched between your fingers.

5 - Take care towards the end to ensure that they don’t burn.