Ingredients 
650g potatoes, I like Vivaldis, peeled and cut into chunks
1 large onion, finely chopped
2 garlic cloves, minced
200g swiss chard, cabbage or brussels
650g leftover cooked gammon or ham, cut into chunks
50g butter
50g flour
350ml milk
200ml water
130ml double cream
1 stock pot
2 tbsp wholegrain mustard
1 tsp english mustard
50g Cheddar cheese, grated
salt and black pepper
a good grating of fresh nutmeg

* If you use chard, remove the stalks and finely cut and shred the leaves

Equipment Needed
2 litre oven dish

Method
Heat the oven to 200c.

Put the potatoes in a pan of cold, salted water and bring to the boil. Reduce the heat and simmer for 12-15 mins until a knife goes through easily. 

Meanwhile heat the oil and 25g of the butter in a pan over a medium heat and cook the onions for 3-5 minutes until soft and translucent.  Add the garlic and chard and cook for another minute or so.  Add the remaining butter and melt.

Add the flour and mix through, cook for a minute to remove the raw flour taste.  Slowly add the milk, stirring all the time and then add the water.  Add the stock pot and both mustards and stir, scraping the bottom stirring until the sauce is thick and glossy.  Add the cream, season with salt and freshly ground black pepper.

Drain the potatoes when cooked and put into the oven dish.  Put the shredded leaves and gammon in the pan.  Pour the sauce over and gently move to make sure everything is coated.  Scatter the cheese over the top and bake for 20-25 minutes until the cheese has melted and is golden.