Many people don't know what they are missing when they cook something in the pan then discard what's left. Those are the most scrumptious bits stuck on the bottom loaded with flavor and are perfect for making pan sauces. In a few simple steps I will give you the keys to making your own pan sauces.
The fist step is to cook whatever it is your are cooking in a large enough saute pan to hold your liquid for your sauce. Use enough fat (oil, butter or a combo of both) to cook your protein, but not so much that you have a puddle of fat left in your pan. If this is the case, then just drain some of it off. After your protein is cooked, remove it from the pan and hold. You now have the foundation for your sauce.
The next step is kind of tricky because it involves the fat left over from the initial step. There should be some fat left from when you first started cooking. The tricky part, especially if it is your first time making a sauce, is to gauge how much fat you need. You are going to use this fat to saute the additives to sauce. The additives add highlights of flavor. They can range from capers or pepper corns, to garlic and shallots, to aromatic herbs and vegetables. When, sauteing these, you should cook them just until you can smell them.
When you can finally smell your additives, then you add liquid such as chicken stock or wine. You don't need a whole lot of liquid. Usually about half to a full cup will do, depending on how much sauce you want to do. When you add your liquid to the hot pan, it will dislodge all the tasty bits that were left on the bottom. You can help the process by stirring the liquid and scrapping the bottom of the pan with a whisk (it will come in handy later as well). This step is called deglazing the pan. Now you just let the liquid reduce by half to 3/4 of its original volume. Some would say let the pan be almost dry, but I think it makes a fuller sauce to have some liquid.
The last step is the hardest because it requires patience. What you are going to do is add butter. This is called mounting a sauce. The butter gives the sauce flavor as well as shine and thickens it up. You will need about half a stick to a stick of butter. The key to adding the sauce is to break it up into small pieces and adding it slowly. Cut the butter into about eight to twelve small pieces. Then whisk the butter in one piece at a time, making sure that the butter is completely incorporated into the sauce before adding the next piece. Another key to the butter is to make sure it is as cold as possible. If you can cut the butter and keep it in the refrigerator until you need it. If it starts to get hot, stick it in the freezer.
After all the butter is incorporated, adjust the seasonings on the sauce. The sauce should be nice and thick and coat the back of a spoon easily. If it is still a little thin, then add a little more butter. If you add too much butter, the sauce will break and be grainy. You can try to fix it by adding a bit more liquid. With a little bit of practice, you can be making pan sauces in no time.