1. Cook the udon in salted water until al dente. Heat the oil in a large frypan over medium heat. Season the salmon well with one teaspoon of salt and fry for about three minutes on each side until lightly browned and just cooked through. Remove from the pan and rest on absorbent paper.
2. Without washing the pan, heat the butter and fry the onion over medium heat until softened. Add the remaining salt and sake and bring to the boil. Add the cream and stir well. Add the udon and stir well, adding a little water if necessary.
3. To serve, top the udon with the salmon roe.