I'd like to make a prime rib soon and I want to develop a very nice jus. Sometimes at restaurants they serve a very dark jus, mine never comes out dark. Basically I roast my prime rib sitting on top of a mix of onions, garlic, celery and carrots that have been tossed with a little olive oil, salt, pepper, and dry thyme. After roasting I add a little beef stock to the pan and reduce, skim and serve. Are there any ingredients I'm missing from my jus? How can I make it more flavorful?