In a large Dutch Oven make a dark roux using the oil and the flour, over low-medium heat. Stirring often to ensure it doesn't stick.
After the roux has become chocolate brown add the diced onions, bell peppers and celery and stir to combine. Turn up the heat a little to medium and continue to cook the vegetables for about 10 minutes until softened.
Add the garlic and cook another 2 minutes.
Slowly pour in the crawfish stock and the water. Stir well and turn up the heat to medium-high.
Add the seasonings, stirring, until a rolling boil has come around. Then turn the temperature down to low-medium and cover.
Allow to simmer for 1 hour, stirring occasionally.
After the 1 hour is up, add the crawfish tails and stir. Turn off the heat.
Allow to sit for 5 minutes then serve over white rice.
Notes
Whenever we have a crawfish boil, and we have leftover crawfish, we like to reserve some of the peelings to make a stock with - as we know we'll be making a crawfish etouffee or a stew like this one and using a nice crawfish stock really adds to the flavor!Add more seasoning as you see fit. This recipe will give you a little kick - depending on how spiced you have your crawfish. We like ours to have a good kick. That will transfer into the stew. If you're using frozen store-bought crawfish tails, then you'll probably have to add more seasoning. Taste as you go.