I made this dish and it was a huge hit in my home...I have tried it with and without shallots and both were delicious. The dish at the cheesecake factory is definitly made with red onions and not shallots however, the recipe posted includes sour cream as an ingredient but does not instruct you when to add it. I have made the dish a few times excluding the sour cream and it was just fine. I would suggest making the dish using different brands of marsala because ultimately that is the key ingredient which determines how flavorful your sauce will be.