In a large stockpot, heat oil over medium-low heat. Add onion, and cook until opaque. Add crawfish shells, celery, bell pepper, and tomato paste; cook, stirring constantly, until caramelized. Stir in wine, and cook for 2 to 3 minutes, scraping browned bits from bottom of pot with a wooden spoon. Add water to cover and crawfish boil seasoning; bring to a boil over high heat. Reduce heat, and simmer for 1 hour. Strain into a large container, discarding solids.
Recipe by Louisiana Cookin' at https://louisianacookin.com/crawfish-boil-potpies/