List of ingredients:
300 gram (2/3 pound) crayfish meat (1,5 kilo/3 pounds unshelled crayfish), or 300 gram (2/3 pound) perchfillet (or tench or lamprey)
200 gram (1 1/2 cup) peeled blanched almonds, ground
150 gram (3/4 cup) rice (uncooked, after cooking about 400 gram/2 cups)
1 Tbsp. sugar
1 tsp. ginger
pinch of salt
some whole crayfish, or heads with claws, to decorate
crayfish shells to make the stock, and a tablespoon olive oil

Preparation in advance:
Shell the crayfish, don't forget to crack the claws if they are fleshy. Put the meat in the refrigerator. Save four whole crayfish or heads with claws for garnish (also: refrigerator).
Rinse shells well under the tap, and drain. Use a third of the shells to prepare the stock for the almond milk, but use the rest to make a concentrated crustacean fumet you can freeze.
Heat olive oil in a pan, fry (as I said, a third of) the shells at high temperature for a minute, then add five decilitres water. Let simmer for 45 minutes, strain the resulting stock.
When making the blancmange with fish, poach the fish preferably on the bone and with skin, fillet when it is done. Save three decilitres of the strained cooking liquid.
Use the cooking liquid (or use fish fumet or crustacean fumet) to make almond milk: steep the (freshly) ground almonds for twenty minutes in the hot liquid. Then strain through a cloth, be sure to press the almond pulp to get as much almond milk as possible.

To prepare:
Chop the crayfish meat. Don't forget to remove the intestine first, unless you get a kick out of eating crayfish poo. Put meat, rice, sugar, salt and ginger in a skillet, and add enough almond milk to moisten the rice. Heat over a low fire until the almond milk has been absorbed or evaporized. If you want to, you can use a blender to purée the rice, but this is not necessary.
Line a pudding mould with plastic foil, scoop in the blancmange, and let it cool to room temperature. Or line small cups or soufflé moulds with plastic foil to get individual portions.

To serve:
Demould the blanc mange on a dish. Use whole crayfish, or the heads and claws, to garnish. You can also use flowers or herbs. Just not slices of lemon. Lemons were an extreme rarity in fourteenth century England.