1. Combine salmon, cornflake crumbs, green onions, celery, 1/4 cup mayonnaise, 2 Tbs. thyme, and Worcestershire sauce in medium bowl and stir gently to blend. Season with salt and pepper. Mix in egg. Shape salmon mixture into 6 patties, about 3/4-inch-thick. Arrange on plate.
2. Combine 3/4 cup mayonnaise, lemon juice, horseradish, and 2-1/2 tsp. thyme in small bowl. Season sauce with salt and pepper. (Salmon cakes and sauce can be prepared 1day ahead. Wrap separately and refrigerate.)
3. Melt butter in heavy large skillet over medium-low heat. Add salmon cakes and saute until brown and cooked through, about 5 minutes per side. Transfer to platter. Serve with sauce.