Serves 8 | prep 20 mins | total time
- 2 large red onions
- 1 tsp olive oil
- 1⁄2 tsp caster sugar
- 2kg floury potatoes, such as Maris Piper, peeled and cut into chunky pieces
- 75g butter
- 175g Swiss Gruyère, finely grated
- 75g extra mature cheddar, finely grated
- 75ml milk, optional
- 125g ready-grated mozzarella
The mash will keep warm in a covered pan for about 30 mins. The caramelised onions can be made a few hours ahead then reheated in the oven alongside the ghoul-ash at 150°C, fan 130°C, gas 2, for 15 minutes.
- Preheat the oven to 190°C, fan 170°C, gas 5. Trim the minimum possible from the root and top of each onion, then cut each into 8 wedges, keeping them attached at the root end. Carefully peel off the skin. Gently mix the onions with the oil, sugar and some seasoning and spread out in a roasting tin. Roast in the oven for 20 minutes, turning halfway.
- Meanwhile, add the potatoes to a large pan of salted boiling water and cook for 20-25 minutes until tender. Drain, then return to the pan and mash with the butter and some seasoning. Beat in the Gruyère and cheddar with a wooden spoon, adding some milk if you like your mash to be a softer consistency. Spoon the mash into a warmed dish and stick in the onion wedges. Keep warm.
- For the 'cobwebs', preheat the grill to high and line a baking tray with baking paper. Scatter the mozzarella evenly over the tray. Grill for about 2 minutes or until the cheese has just melted. Don't grill the cheese for too long or it will go past the stringy stage and start to set. Once melted, quickly pick up bits of cheese with a couple of forks and stretch them over the mash and onions so they look like cobwebs. Serve straight away.
Tip Instead of onion wedges, you can chop up a bunch of spring onions and soften in the 75g butter from the recipe for 5 minutes, then fold into the mash with the cheese.
Cheesy mash is studded with caramelised red onion 'monster claws' and strewn with cobweb-like strings of melted mozzarella.