2 horseradis Recipes

mayonnaise, white horseradish, prepared, butter (1/2 stick, divided ), beef tenderloin steaks, thick, onions, thinly sliced, shiitake mushrooms, stemmed, caps thinly sliced (about 5 cups), beef broth, croissants , halved horizontally, lightly toasted, arugula

waxy potatoes scrubbed, salt, plain yogurt, extra virgin olive oil, minced peeled fresh horseradish, freshly ground black pepper, watercress