This was a recipe shared w/ me by my mother. I loved it when she made this when I was growing up, and was shocked to see how simple it was. You can add whatever you like to the recipe, it's very versatile. Saute any added veggies in the melted butter @ the beginning of recipe. Photo from internet, but it represents how this recipe/sauce should look.
In 4qt pot (I prefer cast iron), melt butter. Add onion, bell pepper. Saute til crisp-tender.
Once veggies have cooked down, add soups and frozen crawfish. Season w/ salt, pepper, and garlic. Adding creole/cajun seasoning, if desired. Cover and simmer, stirring occasionally to prevent burning and to break apart crawfish. Add water anytime during cooking process if you feel it's needed.