When you start to get some caramelization on the veg and the onions are transparent. Of course it is depending on what kind of a sauce you are making. If you are making a clear stock you don't want to brown the vegetables. Some chefs, like Paul Prudhomme, will tell you that vegetables will impart a different flavor profile at different stages of cooking, so he adds them at different times while building the sauce. Break a Spoon!
7/24/09 at 6:29pm