Sea urchin gonad purée

"The gonads of sea urchins are rubbed through a sieve and mixed with an equal volume of thick béchamel sauce (or the two are blended in an electric blender). The purée is simmered for about 5 minutes and some butter is stirred in. For hors d'oeuvres this purée may be spread on croutons fried in butter, sprinkled with grated Parmesan cheese, and browned under the broiler. It can also be used to fill small vol-u-vents or the like."