Parboil the potato and carrots for 5 minutes, then drain and cool a little. Peel the potato.
Grate the potato and carrot into a sieve. Sprinkle the flour and lots of seasoning on top and shake the sieve so it coats all the veg.
Add the spring onion and shape into two discs.
Heat some butter in a frying pan. Add the rostis one at a time and fry gently until the bases brown. Flip to cook the other side, adding more butter if you need to.
Slide onto 2 plates and fry 2 eggs in the pan, adding one to each plate. Serve with green salad.