Start by melting 1/2 cup of butter in a large saucepan over medium heat.
Add in 1/2 cup of flour slowly, stirring continuously to create a roux.
Reduce heat to medium-low and cook the roux until it turns a deep, mahogany color.
This process can take about 20-30 minutes, but patience will reward you with a rich base.
Add the chopped bell pepper, celery, and garlic to your roux.
Stir everything together and sauté these veggies until they become translucent.
Pour in 3 cups of seafood stock gradually while stirring to combine it properly with the vegetables and roux.
Add the bay leaf, cayenne pepper, salt, and black pepper to the mix.
Stir in the crawfish tails and chopped green onions, letting everything simmer for about 10-15 minutes.
The etouffee should thicken nicely and develop a full flavor.