1. Heat your oven to 200C/Gas Mark 6 and grease a large baking dish then leave to one side.
2. Put the quartered potatoes in a large pan of salted water and bring to the boil. Simmer for approximately 10 minutes or until just cooked.
3. Whilst waiting for your potatoes to boil, melt half the butter in a frying pan and cook the onion with a sprinkling of salt until soft.
4. Drain the potatoes and return to the pan. Add the remaining butter and milk then mash together until smooth (or as smooth as you want). If you’ve got a few drops of cream in the fridge that need using up then don’t be shy to throw this in. It’s a bit naughty but will only make your mash tastier.
5. Add the fried onion, mustard, beaten eggs and 200g of the grated cheese and stir together until it is all combined. Season with salt and pepper.
6. Transfer to the baking dish and top with the remaining cheese. Bake in the oven for 20-30 minutes or until the top is golden brown. You want to end up with a crispy, gooey cheesy top and a soft, smooth potato mash filling. Serve with some wilted kale, spring greens, or spinach on the side.
Spruce it Up
Cheddar is the go to cheese here but you can change it to suit your needs and what you might have in the fridge. From parmesan or gruyere to a mix of both. Don’t go out of your way to buy cheddar if you have something else in the fridge.
This is also a great way to use up anything you might have past its best in the fridge: A few mushrooms that may have been left at the bottom of the fridge and be diced and thrown in when you fry the onions or a sprinkling of parsley or chives mixed into the mashed potato works a treat.