Mix about a quarter cup of flour, some salt and pepper and perhaps some dried herbs in a shallow bowl or plate and dredge each piece in the flour. A light coat works best. Save the seasoned flour to use in the gravy.

In a large skillet, heat a quarter cup of olive oil over high heat. Place the medallions in the pan without crowding them and leave them alone to brown. Turn them when they are a nice golden brown color and brown the other side. The idea is to sear the outside of the meat rather than cook it all the way through. When both sides are nicely browned, remove the medallions to a plate and let them set while you make the gravy.

After removing the meat you'll have some oil and pan drippings left in the skillet. To make two cups of gravy you'll want about 3 tablespoons of fat. You don't have to be exact, just eyeball it. Pork tenderloin is very lean, you can add a little more olive oil or a pat of butter if you need more. I added about a tablespoon of butter to the pan above and turned the heat to low while waiting for it to melt.

Use about 3 tablespoons of the flour leftover from dredging and stir it into the butter/fat/oil in the skillet. You'll notice it will quickly form a paste. The paste is called a roux and that's what we want. After it's cooked for a minute or two and has started to change color, add about 1/2 cup of chicken broth to the pan and stir to dissolve the roux and the brown bits at the bottom of the pan into the broth. It will get really thick. Add another 1/2 cup of broth and stir again. When it starts to thicken up, add the another 1/2 cup of broth (1 1/2 cups total at this point). Finally, add 1/2 cup of sherry (or a dry white wine) and stir well.

Let the gravy bubble and simmer for a bit and thicken up. Taste and adjust the salt and pepper and add some dried thyme or rosemary if you like, then return the pork medallions and any juices they may have released to the pan. Put the lid on and gently simmer for another 20 minutes or so until the medallions are cooked through. Pork can be faintly pink when you cut into it, but if it's oinking it's not ready.