Prepare the sauce. Melt lard in a medium saucepan, add chili powder, onion, bell pepper, celery and garlic. Cook over medium heat until soft, about 10 minutes. Add corn or instant flour and cook 2 minutes more. Add cream and stock, bring mixture to a boil and stir in cheddar cheese. Stir constantly until melted. Remove sauce from heat and season to taste with salt. Heat oven to 200ºC then prepare the enchiladas. Soften tortilla shells by wrapping them in plastic wrap and heating in a microwave oven for 30 to 50 seconds. Combine half of the sauce with the crawfish tails. Fill each tortilla shell with quarter cup of this mixture and sprinkle with green onion. Roll shells around filling and fit snugly into a small oven casserole dish. Pour remaining sauce over all and top with shredded Monterey Jack. Bake until enchiladas are heated through and cheese is melted and bubbly, about 10 minutes. From chef Greg Sonnier, Gabrielle's Restaurant, New Orleans.