1. Preheat your oven to 200°C/Fan 180°C/Gas 6. Scrub the potatoes and pierce them all over with a fork. Pop them on a plate and cook in your microwave on high for 8-12 mins (no microwave? Jump to step 2). When they’re tender to the touch, use oven gloves or tongs to put them on a baking tray.
2. Drizzle each potato with 1 tsp oil and season with a little salt and pepper. Slide the tray into the oven and bake the potatoes for 30 mins till cooked through – or bake for 1 hr 30 mins if you don’t have a microwave. Test them with a skewer to check they’re soft all the way through.
3. While the potatoes bake, trim the roots and woody greens from the leeks. Rinse out any grit and finely slice them. Pour ½ tbsp oil into a medium-sized pan and add the leeks. Season with salt and pepper. Pop a lid on the pan and sweat the leeks over a medium heat for 8-10 mins, stirring occasionally, till they're glossy and starting to soften.
4. Finely slice the kale leaves off their woody cores. Finely slice the leaves. Coarsely grate the cheddar.
5. Add the kale to the leeks with 2 tbsp water. Cook, stirring, for 3-4 mins till the kale has wilted and become a dark, glossy green. Scoop the veg out of the pan and into a bowl. Set aside.
6. Pop the pan back on a medium heat. Add the butter and melt it, then tip in the cornflour. Cook and stir for 2 mins till the butter and cornflour are smoothly combined – this is your roux.
7. Add the milk to the roux, a splash at a time and whisking well between each addition until the milk and the roux are smoothly combined. When all the milk has been added, turn the heat up and bring to a bubble. Take the pan off the heat. Stir in the grated cheddar.
8. Meanwhile, separate the egg yolks from their whites and tip the yolks into a bowl (see our tip for ways to use up your egg whites). Add the Worcester sauce and mustard to the egg yolks and whisk together.
9. Add the egg yolk mix and the leeks and kale to the sauce and stir till well combined. Taste and add a pinch of salt and pepper, if you think it needs it.
10. The potatoes should be tender all the way through by now. Halve them and scoop out the flesh. Pop into a bowl and mash. Heat your grill to medium-high.
11. Mix the cheese rarebit sauce into the mashed potato. Spoon the cheesy mash back into the potato skins. Grill for 5-8 mins till golden brown and bubbling (you can also leave the oven on and bake the stuffed potatoes for 15-20 mins, if you prefer).
12. While the welsh rarebit jacket potatoes grill, trim the spring onions and finely slice them.
13. Serve the Welsh rarebit jacket potatoes garnished with the sliced spring onions and with a mixed salad on the side.
14. Get Ahead
You can make the welsh rarebit sauce up to 5 days ahead and keep it in the fridge in a sealed tub. Follow the steps to kake the sauce, adding the egg yolks, kale and leek, then transfer to a tub, cool, seal and store in the frdge. You can use the sauce bit by bit to make individual stuffed jacket potatoes, or spread it on bread and bake in the oven to make welsh rarebit on toast. You can also assemble the stuffed jacket potatoes, cool and store them in the fridge the night before you want to cook them. The next day, bake them in the oven set to 180°C/Fan 160°C/Gas 4 for around 30 mins till golden and cooked through.
15. Love Your Leftovers
The stuffed jacket potatoes will keep for up to 3 days in the fridge. Cool them, then transfer to tub, seal and store in the fridge. Reheat in the microwave or oven till piping hot all the way through.
16. No Waste, More Taste
Your leftover egg whites can be kept in the fridge for up to 2 days or frozen for up to 3 months. Transfer them to a freezer bag or ice cube tray and freeze till solid. Defrost completely before using – they're great whisked till stiff, then whisked with 100g sugar to make a meringue. Bake till crisp and serve with fruit and cream.