Halve the kipfler potatoes.
Peel and cut the onions into wedges.
Pour the vegetable stock into a flameproof casserole dish on a low heat and add the saffron, onions and fennel. Cook for 20 minutes over low heat.
Mix the cream with the egg yolk and pour into the casserole dish off the heat: the mixture mustn’t boil after this point.
Season with salt and pepper.