Melt the butter in a large skillet over medium-high heat. Add the flour and cook until the roux is a peanut butter color, about 5 minutes. Add the onions, celery, and bell peppers and saute until soft and golden, 10 to 12 minutes. Add the crawfish and bay leaves. Reduce the heat to medium. Stirring occasionally, cook until the crawfish begin throwing off a little liquid, 10 to 12 minutes.
Add the chicken stock to the crawfish mixture and season with salt and cayenne pepper. Stir until the mixture thickens, about 4 minutes. Add the parsley and green onions and cook for about 2 minutes.
Remove the bay leaves and serve over cooked white rice.