Not something I know how to do, but I can make a roux, and even though we didn't have two parts of the southern trinity -- bell peppers and celery -- I did have onions and garlic.
Generally, one makes the roux -- flour and butter, in more or less equal parts -- and cooks the trinity separate, marrying them with the protein in a threesome and adding other bits. Crawfish is even tastier, by hard to come by up here.
Because I had a large skillet, I was able to cook the onions and garlic -- finely chopped -- shove them to the side, make the roux, and mix 'em together in the same pan. I did what is called a blond roux -- you can cook it anywhere from white to almost black, and blond is good for this kind of dish.
To this, I added a pound of peeled shrimp, some diced tomatoes and water, and seasoning, primarily Tony Chachere's Original Creole Seasoning. (That's pronounced "Sah-shoo-ray.") Along with some pepper and salt.
Doesn't take long, under thirty minutes from start to finish, not counting the rice, over which you ladle the shrimp.
This is is a keeper, something I'd do for company ...