Preheat the oven to 180°C.
Butter the bread and spread with 1 tsp of mustard to assemble four ham sandwiches.
Cut sandwiches into circles or triangles and place them in a small oval ovenproof dish.
Drizzle the ale over the sandwiches if using.
Bring the cream to a boil in a pan until it thickens, then remove from heat.
Stir in the remaining mustard, Worcestershire sauce, egg yolks, and 225g of cheese.
Season the sauce with salt and pepper.
Pour the sauce over the sandwiches and sprinkle the remaining 55g of cheese on top.
Bake for 12 minutes until golden-brown and bubbling.
Serve immediately with dressed salad leaves.