Learn how to avoid these common mistakes for success every time.
One cause is the direct dumping of dry flour, cornstarch, or other thickener into the hot stock or broth. Another: adding broth too quickly into a roux—the flour-fat mixture that some gravy recipes start with—which can cause clumping or a gluey layer on the bottom of the pan. Hot spots in a large pan can complicate things, as well. In any starch-based sauce, the thickener needs to be gradually introduced to the hot liquid it's supposed to thicken. The easiest way, as with our recipe for the Mushroom Gravy, involves whisking a flour slurry into the broth mixture, then stirring until the gravy comes together.
If lumps happen, pass gravy through a sieve or strainer, or puree it (with an immersion blender or, very carefully, in a regular blender). If the gravy originally contained sautéed mushroom slices, well, the guests needn't know that, and it will still be delicious.