Put into blender: fish, 1 cup milk, potato starch, eggs, and seasonings.
Cover and blend on high speed until thoroughly blended (about 2 minutes).
Remove cover and, with motor on, pour in about 1/2 cup milk, or enough to fill container 3/4 full; pour in 1 cup heavy cream.
Immediately turn off motor.
Pour into buttered quart mold; set in pan containing about 1 inch warm water.
Bake in a 325° oven one hour or until set in center.