Mix the hollandaise sauce with the mustard and set aside. Heat a small frying pan until hot, add the ham and dry-fry for 2 minutes on each side until crispy. Meanwhile, spread the muffins with some of the butter and keep warm.
Brush a nonstick frying pan with the remaining butter and place over a moderate heat until hot. Break in the eggs and cook for 2 minutes.
Divide the muffin halves between 2 plates, arrange the eggs on top and spoon over the sauce. Serve immediately with the crisp ham and salad leaves.