Heat your oven to 180°C/Fan 160°C/Gas 4. Slice the tops off the pattipans, about a quarter of the way down, to form lids. Scoop out and discard the seeds. Scoop out the flesh from the lids and bases, leaving a ½cm wall of squash behind.
Finely chop the pattipan flesh. Pull the husks and silky threads off the sweetcorn cob. Stand the cob upright on a board. Run a knife down the sides to slice off the kernels. Peel and finely slice the onion.
Warm 1 tbsp oil in a large pan over a low heat. Add the onion and a pinch of salt and pepper. Cover and cook for 10 mins till soft but not coloured. Stir often.
Tip the chopped squash into the pan. Cover and cook for another 10 mins till the squash has started to soften. Chuck in the sweetcorn and cook for another 5 mins till everything is tender.
Stir the mixed spice and paprika into the veg with a pinch of chilli powder (it's hot, so use as much or as little as you like). Crumble in the feta and stir well. Taste and add more salt, pepper or spices if you think it needs it.
Carefully separate the egg yolk from the white (keep the white for making meringues another day). Beat the egg yolk and milk in a bowl, then sprinkle in a little salt and pepper.
Place the hollowed-out pattipans in a roasting tin. Spoon in the veg mix, dividing it equally between the squashes. Spoon over the milk and egg mix. Cover the pattipans with their lids. Bake for 30 mins till they’re tender all the way through.
Meanwhile, tip the pearl barley into a pan and add 300ml boiling water. Return to the boil, then reduce the temperature, pop a lid on the pan and simmer for 20 mins, till the grains are tender. Stir in a little salt and pepper.
Pour 1 tbsp oil into a small frying pan and bring to a medium heat. Scatter in the sage leaves and fry for 1-2 mins, turning once, till crisp. Serve the stuffed pattipans with the pearl barley on the side and topped with crisp sage leaves.