Regardless on the size of your crayfish, they are best cooked whole. This way the carapace acts like an oven itself, whereby the shell heats up and bakes the flesh inside.
However, if you are cooking a fairly large crayfish it's advisable to split it down the back with a sharp heavy knife. This will help it to cook quicker and make it more manageable to serve once it's cooked.
I love cooking it on a barbecue, but it can be cooked just as well at home under a domestic grill, if split in half. Cooking times will vary, but a whole crayfish of around 1 to 1 3/4 pounds will take about 15 to 20 minutes above a hot barbecue, turning it around to cook through evenly. If the crayfish is halved, it will take between 10 to 15 minutes. A large crayfish, around 2 pounds, will take 25 to 35 minutes and if split, about 15 minutes.
Serve grilled crayfish very simply with a little olive oil and lemon juice, or melted butter. However, the following dressings add a little oomph to this delicious meat.
Place all of the above in a blender and puree to a thick dressing. Taste for seasoning, then let rest for at least 30 minutes before serving.
Heat the butter in a small pan, when it?s bubbling add the onion and chile and cook over a moderate heat until the onion just begins to soften, about 2 minutes. Take it off the heat, stir in the juice, cilantro, and salt. Serve immediately.