In one sentence, describe what the following article is about:

While this heats up, mince the garlic and chop up onions and mushrooms, if desired. The garlic should be slightly golden. Add any mushrooms and onions as well, along with a tablespoon of butter. Cook another 5 minutes, or until the onions are translucent (slightly see-through) Use a wooden spoon to stir and scrape up any bits of caramelized onion from the bottom of the pan. The heat should be on medium-low. This is the "reduction" phase. Use you fingers to lightly mix the flour into the butter. Set this aside. There should only be a little bit of wine remaining -- roughly a fourth. Add the broth and bring the liquid back to a simmer. It can help to preheat the broth in a microwave before adding it. Add the butter a little bit at a time, stirring the whole time with a spoon. The longer it simmers, the thicker the sauce will become. The sauce is incredibly versatile, and goes well with vegetables and white meats or fish. If you want to add shellfish, like shrimp or clams, add them with the garlic to cook with the sauce.
Heat up the oil or butter in a saucepan on medium heat. Cook the garlic in the hot oil for 1-2 minutes. Add the white wine and reduce the heat to a simmer. Mix the flour and remaining 2 tablespoons butter in another dish. Add the broth to the saucepan once the wine has almost evaporated. Slowly stir in the butter/flour mixture. Add any seasonings and let the sauce simmer for 4-5 minutes. Serve over pasta, chicken, or shellfish.