White Grits
Bring the water to a boil and lightly season with salt. Add the grits while stirring rapidly and reduce heat to low. Simmer the grits for about 20 minutes, stirring constantly to prevent them from sticking to the bottom of the pot.
To finish, turn off heat and stir in butter and Mascarpone cheese.

Crawfish Stock
To a large pot, add celery, carrot, onion, thyme, garlic, shells, and just enough water to cover the other ingredients. Simmer on low for 1 hour, skimming the fat off throughout the hour.
Strain and reserve liquid in refrigerator.

Sautéed Crawfish and Sauce
Heat a large pan over medium heat and add the olive oil. Season the crawfish tails with Creole spice and salt and sauté until they start to brown but are not cooked all the way through. Remove the crawfish and hold on the side.
To the pan add the Andouille sausage, garlic, shallot, Piquillo pepper, and thyme, and sauté until they become aromatic. Add the stock and bring to a low simmer. Stir in the butter and reduce until thickened. Add crawfish back to the pot and cook through.
Finish with tomatoes, chives, and lemon juice.

Serve
For each serving, place 4 tablespoons of grits in the middle of a large bowl.
Divide the crawfish evenly atop the grits and spoon the sauce around to fill in the negative space.
Garnish with fresh chervil.