Salt the fish on a plate and let sit for about 10 minutes.
On a second plate or a shallow bowl, mix together flour, salt, garlic powder, and pepper to taste. Keep in mind that the fish is already salted, so you won't need much to flavor the coating!
Coat the fish in the flour mixture and let it sit on the plate for about 5 minutes.
Preheat a pan over medium heat (we like to use a cast iron pan). Add vegetable oil and once it is hot enough to start sizzling, add each piece of fish to the pan, dusting off any excess flour before adding it.
Cook for about 5 minutes on each side until the fish is opaque in the center and a golden crust has formed.
While the fish is cooking, make your parsley sauce by melting butter in a pan and whisking in flour to create a roux.
Let the flour and butter cook for about a minute (take care not to burn it!).
Add the milk a little bit at a time, whisking constantly to create a smooth sauce.
Make sure the sauce comes up to a boil so the flour has a chance to fully thicken the sauce. Season to taste with salt, pepper, and nutmeg (optional).
Chop up parsley and add to the sauce, letting it cook for about a minute. Check for seasoning.
Serve fish and sauce with your favorite side (we like to serve it with roasted potatoes!). You can also use this sauce with other meats, such as roast pork or beef.