Preheat oven to 180°C.
Combine KEEN’S mustard powder, ricotta cheese, gruyere cheese, nutmeg, salt and pepper. Divide and spread onto 4 slices of bread. Top with shaved ham and remainder slices of bread.
Melt the butter in a frying pan on medium heat and fry each sandwich until golden brown on both sides then place in oven for 5-10 minutes until cheese mixture is melted. Serve hot.