Slice the onions into thin strips and add to a large frying pan with one tablespoon of olive oil.
Keep the onions on medium low heat and stir throughout the caramelisation adding the sugar half way through. This can take around 30 minutes for fully caramelised onions so have patience for the finished product!
Peel the potatoes and chop into even sized cubes.
Boil the potatoes in salted water until soft. To test the potatoes take out the biggest cube and try to crush with a fork. Make sure it is super soft and easy to mash.
Drain the potatoes and return to the pan to mash.
To the potatoes add the butter, garlic, salt, pepper, cheese and parsley.
Mash until smooth.
Fold in most of the caramelised onions saving some for the topping.
Once all combined serve up topped with a knob of butter, more cheese, the rest of the caramelised onions and sprinkle on some parsley.