Adjust the oven rack to its lowest position, and preheat the oven to 425 degrees F.

Arrange the asparagus into 4 bundles of 5 spears on 2 pieces of parchment paper. Season the asparagus with salt and sugar (for caramelizing), and then drizzle with the melted butter. Fold the grease parchment paper like a book, and seal it with paper clips. Put the parchment paper packages next to each other on the oven rack (do not use a baking sheet). Bake for 15 to 20 minutes, or until sugar has caramelized.

To plate, cut open the parchment paper packages, and top with the crayfish and their sauce.

Crayfish:

Bring a large pot of water to a boil, and then add the sea salt, garlic, cumin, peppercorns, star anise, bay leaf, celery, shallots, fennel, and chile. Reduce the heat and let simmer for 10 minutes. Remove from heat and set aside. This will be used as the stock to cook the crayfish.

With a spider or slotted spoon, remove the vegetables from the stock. Bring the stock back to a boil for another 10 minutes.

In another large saucepan of boiling salted water, place the crayfish, which are still alive at this point, and cook for 30 seconds. Remove them to an ice water bath to cool them and prevent further cooking. Remove them from the water bath, turn their tails, and pull to remove the intestines. Then, add them to the stock and cook for several minutes, or until cooked through. Cool them in the ice water bath, and then peel them with a pair of scissors.

In a large skillet, brown 1/2 cup of butter. Add the peeled crayfish, lime juice, and chervil, tossing to coat well.