The sauce can be refrigerated for 1 week. Reheat gently. The cooked shallots can be removed from the oil and kept for 6 hours, then reheated; save the shallot oil for frying.
Veal stock and fleur de sel are available at specialty food stores and some supermarkets. Fleur de sel can be mail-ordered from dartagnan.com.
A young red Bordeaux has enough tannin to cut through the fattiness of the steak and enough rich Cabernet-Merlot flavor to blend with the shallots.