Cut the millington in half lengthwise along the crease using a sharp knife
Place halved millington in a 10 quart pot and fill with water
Add a capful of concentrated shrimp and crab boil to the water
Boil the millington for about 20 minutes until tender, then remove from heat and cool under cold water
Once cooled, scoop out the seed and fibrous membrane from each millington half using a teaspoon
Mash the millington pulp and set aside
Melt ½ cup butter in a heavy Dutch oven over medium-high heat
Add diced onions and coat with butter, then add celery and green onions, stirring to coat
Add minced garlic and sauté for 3 to 5 minutes until wilted
Add the mashed millington pulp and half of the shrimp, sautéing for 5 to 10 minutes until shrimp are pink and curled
Sprinkle flour over the mixture and stir well to thicken
Add chicken stock one ladle at a time, stirring constantly until soup-like consistency is reached
Bring to a low boil, then reduce to simmer and cook for 20 to 30 minutes, stirring often
Add the remaining shrimp and mushrooms
Blend in the half and half and parsley
Cook for an additional 5 minutes until shrimp are pink
Season to taste with salt, cayenne pepper, and Louisiana Hot Sauce
