*Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.
**Nutrient information is not available for all ingredients. Amount is based on available nutrient data.
(-)Information is not currently available for this nutrient. If you are following a medically restrictive diet, please consult your doctor or registered dietitian before preparing this recipe for personal consumption.
Whisk together the mayonnaise, Dijonnaise and horseradish in a small bowl, season with salt and pepper.
Heat a grill pan or griddle over medium heat. Add 3 slices of beef in an even layer, next to each other and cook for 30 seconds per side, just to warm through. Top the slices 1 or 2 slices of the cheese, cover with a lid and let melt, about 20 seconds.
Spread some of the mayonnaise on each both sides of each croissant. Layer on beef, cheese, onion and watercress.
*Or you can grill your own marinated flank steak: Flank Steak – let marinate for at least 2 hours and up to 24 hours. Heat a grill to high or a grill pan over high heat until smoking. Season the steak with salt and lots of black pepper and cook on both sides until golden brown and slightly charred and cooked to medium-rare doneness, about 6 minutes per side. Remove from the heat and let rest 10 minutes before slicing into thin slices against the grain of the meat.