The basis of crawfish etouffee, like many Louisiana soups and dishes, is a roux. A roux is essentially a mixture of flour and oil (or sometimes butter) that is used to make a gravy or sauce. While some crawfish etouffee recipes call for a darker, almost brownish gravy, many traditional eateries in and around New Orleans use a gravy that is more reddish in color. The ingredients in a red roux for crawfish etouffee are simple, but making a roux is, perhaps, more art than science. If it doesn't come out quite right the first time, give it another go.
Heat a skillet on high heat and add a stick of butter. Allow the butter to melt completely. Heat the butter just to the point where it begins to brown slightly, but be careful not to let it burn.
Slowly add 1/2 cup flour, stirring it briskly into the butter with a plastic whisk. Don't just dump all the flour in at once. Add it gradually as you continue to mix, allowing it to lightly brown into a buttery, dough-like consistency.
Reduce the heat from high to just above medium, while continuing to stir.
Add a 6 oz. can of tomato paste. Stir it well, until it's blended completely into the flour and butter mixture. The consistency should be thick and pasty, almost like a dough.
Add 1 cup of white wine or cooking sherry. Pour it in gradually as you stir it into the mix. This step should transform the dough-like consistency of the roux into more of a gravy-like texture. It is important to continue to stir the mixture throughout this process. If, once the wine is completely stirred in, the mixture is still too doughy, you can add a dash or two of water.
Once made, the red roux can be used immediately for crawfish etouffee or stored in a container and frozen for later use.