There are several key things worth knowing if you want to create a pan sauce that's as good as one you'd find at a restaurant. For the most common style of pan sauce—that is, one made primarily with stock—you should follow the tips Kenji has already outlined: Use a stock that's rich with gelatin to create a sauce with good body that emulsifies well, and round it out with butter. For a creamy-style pan sauce, look to my explanation on how heavy cream alone can be enough to create a sauce with lots of body.
Now I'd like to toss one more trick your way: fiber. Let's say you're making a simple pork chop dinner at home one night. You have some store-bought stock, notoriously devoid of gelatin, and you realize that your stash of unflavored gelatin is totally depleted from that delicious chicken with lemon-rosemary pan sauce you made a few nights before. You don't have any heavy cream in the fridge, nor crème fraîche, sour cream, or any other ingredient that might stand in for it. What do you do?
If you were me (or should I say, if I were you), I'd look to fiber. No, I don't mean you should spike the sauce with capsules of Metamucil that have been keeping...er...things so regular. I mean vegetable fiber.
Let's take tomato sauce as an example. Ever think about what makes it so thick that it can cling to noodles in such a satisfying way? Some of you whiz-kids of there will undoubtedly say pectin, and you'd be right. But pectin is actually just a soluble dietary fiber. And even without the pectin, all the other fiber that makes up the structural, non-watery parts of the tomato will still be there adding body and texture to the sauce. Pass tomato sauce through a fine enough strainer so that you've removed all the rough fiber, and all you'll be left with is watery tomato juice—not exactly what you'd want to toss on pasta.
You can apply this idea to a pan sauce by using vegetable matter to thicken what might otherwise be a too-thin consistency. The recipe I'm sharing here is one example of how to do it.
I start by searing pork chops using the reverse-searing method we often recommend, which helps deliver juicy meat that's blushing pink throughout while reducing your chances of overcooking the chops. The method starts by slowly cooking the chops at low heat in the oven until mostly cooked through, then searing them in a pan until browned and crisp all over and perfectly cooked within.
I always like to lift the chops and sear the rim of fat that runs along the outer edge of the loin. That helps to render some of the excess fat out of them, while crisping it up, making it much more pleasant (and, frankly, delicious) than if it were just a sad old blob of fat that hadn't been seared first.
Once the chops are done and resting, I sauté plenty of chopped leeks (about 1 1/2 cups for just two pork chops) along with a little garlic. Leeks have a beautiful way of softening to the point of nearly melting as they cook, and that's what I'm going for here: They are, in essence, the thickening element of this sauce.
Once the leeks and garlic are tender, I add white wine and stock and let it reduce slightly. If your stock does have gelatin, all the more power to you. But if it doesn't, the leeks are going to give your sauce the body it needs, both through their added fiber and through the turbulence they add to the pan as you're stirring the sauce, which can help to form a more stable emulsion.
To round out the sharp flavor of the wine and to help add just a bit more richness, I whisk in a bit of butter at the end along with some lemon zest to add just a little more life and dimension to the whole thing.
It's an incredibly simple way to add substance and body to a sauce that might otherwise have none. And of course, it doesn't just work with leeks. Tomato sauce, as I mentioned, is a natural in this area, as are all sorts of fruit and vegetable purées: A few spoonfuls of apple sauce, say, or pureed roasted squash or broccoli, will do wonders for an otherwise watery pan sauce. Apricot or fig jams are a great base for a sweet-savory sauce for pork or chicken. Depending on the form of the fiber you add, different degrees of refinement are possible—chopped leeks like this, or a chunky tomato sauce, will give a more rustic texture, while a smooth squash purée that's been worked through a fine mesh strainer can make an elegant, silky-smooth sauce.
The power is in your hands now, there are no longer any good excuses for a weak, watery pan sauce.