Peel the crawfish, reserving about 3 pounds worth of heads and shells. Add to a large stock pot and cover with 12 cups water. Add garlic, onion peel, carrot, celery, bay leaf, thyme, and parsley. Stir and bring to a boil. Reduce heat to a simmer, and simmer on medium heat for 30 minutes.
Strain through a fine mesh strainer and reserve stock.
To make the bisque:
Heat the butter in a soup pot or Dutch oven over medium heat. Add the onion to the butter and saute for 3 minutes, just until lightly softened {don't brown the onion}.
Stir in the tomato paste and garlic. Stir well to mix with the onions and cook about 2 minutes.
Slowly stir in 6 cups crawfish stock until tomato paste is completely incorporated. Add in rice and 1 cup {about 4 oz.} crawfish, and cook for 35 minutes, stirring occasionally, on medium-low. When rice is very tender, remove from heat. Transfer to a blender {making sure to vent the side or use a dish towel to cover opening, so steam can escape} and blend until very smooth, or use an immersion blender.
Transfer mixture back to the soup pot and add 2 cups stock to mixture. Stir well to combine and add in remaining crawfish. Cook for about 5 minutes, adding more stock if needed. Add lemon juice and half & half, if using. Taste and add salt or more lemon juice if needed.
Sprinkle with parsley if desired. Enjoy immediately {for best results}
Notes
*To make stock using uncooked crawfish: Bring a very large pot of water to a boil. Add crawfish and boil for about 10-15 minutes. Pick crawfish and follow instructions for using already cooked crawfish but add 1 tablespoon salt, 1 quartered lemon, 1 teaspoon cayenne pepper, 1 chopped onion, an extra clove of garlic, and a few extra sprigs thyme.*The nutrition facts are likely off because I couldn't calculate the amount in the homemade stock, so I used homemade fish stock in the nutrition facts which might make it a little different.*Inspired by The Plantation Cookbook by The Junior League of New Orleans and Hunter Angler Gardener Cook Blog