Chop all of the vegetables into small dice and place them in bowls near the stove before you begin. 

Place the stock in a separate small saucepan near the stove and keep warm. The stock doesn’t have to be piping hot to add to the roux, but it cannot be cold. 

In a large, heavy-bottomed stock pot add the oil and flour. (You may replace 2 tablespoons of oil with bacon fat for extra flavor if you keep your bacon grease.) 

Over medium heat, whisk the flour and oil mixture until creating a blonde roux. This occurs when the flour and oil combine and are light yellow in color. 

Switch to a high temperature spatula or wooden spatula to scrap the bottom of the pan with greater ease as it cooks. 

Continue stirring the roux as it goes from light brown to a peanut butter color to a rusty brown, and then finally to a dark roux. You may have to turn the heat down as the roux darkens to prevent burning. Never leave the roux alone or walk away from the pot or it will burn and you will have to start over. 

Get the roux as dark as you feel comfortable and prepare to move rapidly. Turn the heat down to low if it isn’t already there. 

Add the chopped onion and toss well. (As you add the vegetables the roux will steam, darken, and bubble wildly.) Cook 1-2 minutes. Add in the celery and green bell pepper and cook an additional minute. Add the garlic and cook 30 seconds, mixing well. 

Switch back to your whisk and gently pour in the stock, in small increments, whisking well as you go. 

Add the cajun seasoning, thyme, white pepper, and bay leaves, and bring to a simmer.

Add in the crawfish tails and fold gently. 

To taste, add in the hot sauce or lemon juice for acidity, and after tasting add in the teaspoon of kosher salt if needed. You may also season with additional cajun seasoning or red pepper if you like it extra spicy. 

Turn off the heat and keep covered until ready to serve.

Serve atop hot, cooked white rice. Sprinkle with fresh parsley and green onions as garnish.