Put the grated potatoes and zucchini/courgettes in a clean tea towel and squeeze out as much water as you can. Tip into a bowl with the chives, egg yolk, gluten free flour and plenty of seasoning. Mix well.
Heat oven to 180C/160C fan/gas 4. Put a little oil in a frying pan. Divide the mixture into 4 flat röstis and add to the pan (fry as many as you can fit in your pan at once).
Cook over a medium heat for 6-8 mins until the underside is crisp and brown, then flip over and cook the other side. When they’re cooked, transfer to a baking parchment-lined tray and put in the oven.
While the rostis are finishing off in the oven, fry the eggs to your liking, then serve with the zucchini/courgette rostis.