Crayfish with mayonnaise

Steep crayfish in a large container of fresh water to cover, firmly closed, for about 30 minutes.
Pour water to 3 cm deep in a saucepan large enough to hold all crayfish, and add all ingredients except crayfish. Bring to boil, then simmer gently for about 10 minutes.
Increase heat, pile crayfish into saucepan, curling tails underneath. Cover, bring to boil, then steam for no longer than 14 minutes. Do not overcook or crayfish will be dry.
Remove crayfish, cool right side up on a draining board. When cold, refrigerate whole until about 30 minutes before serving.
Halve crayfish lengthways, remove sac at front of head, and intestine.
Serve with lemon, mayonnaise (preferably homemade – see recipe) and garnish with parsley.