When you have finished pan-frying or sautéing your fish or seafood, add 2 more tablespoons of whatever oil or butter you cooked the fish with, scraping any browned bits off the bottom of the pan with a wooden spoon.

Turn the heat to medium-low and sprinkle in the flour and mix well with a fork or wooden spoon. Let this cook and stir often until it turns light brown; you are making a roux (pronounced "roo" in case you were wondering). It is very important not to burn the roux, so watch it closely.

When the roux is light brown, add the wine. It will sputter. Mix well and scrape any browned bits off the bottom with the wooden spoon. This is important because all the flavor lies in the bits, so get them all off the bottom of the pan and into your sauce.

It may thicken up quite a bit immediately, so add the stock and mix well. Bring this to a boil over high heat.

When the sauce has reduced by about half, taste a bit for salt and add more if you need to.

The sauce is done when it can coat the back of a spoon, or when it takes a second or so to fill in after you drag the wooden spoon through the center of the pan. If you really want to get fancy, pour the sauce through a fine-mesh strainer before serving. This will remove any bigger bits, but is not a necessary step for an at-home recipe. Serve the fish immediately, with the sauce either poured over or served on the side, so it remains smooth and hot.