In a medium Dutch oven, cook bacon over medium heat until crispy, about 10 minutes. Remove bacon using a slotted spoon, and let drain on paper towels, reserving ¼ cup drippings in pot. Reduce heat to medium-low; whisk in flour until smooth. Cook, stirring occasionally, until roux is a light chocolate brown, 10 to 15 minutes.
Increase heat to medium. Add sweet onion, bell pepper, and chopped celery; cook, stirring occasionally, until vegetables are crisp-tender, about 5 minutes. Add garlic; cook until fragrant, about 1 minute. Gradually whisk in stock until smooth. Stir in Cajun seasoning, paprika, hot sauce, salt, and celery seed. Reduce heat to medium-low; cover and simmer, stirring occasionally, until slightly thickened, 15 to 20 minutes.
Stir in crawfish and parsley; cook for 1 minute. Serve over hot cooked rice. Top with bacon. Garnish with green onion, if desired.
Recipe by Louisiana Cookin' at https://louisianacookin.com/smoky-crawfish-etouffee/