Generously butter a 7-inch-diameter soufflé dish and sprinkle the sides with a little Parmesan to aid the rising. Place upside down in the freezer until needed.
Remove the black stringy bits from the roes, and run under a hot tap to firm them up. Fry the roes gently in the butter for 5 minutes.
Work the roes and butter in a blender or a food processor, but do not purée until smo