Crepes: Whisk eggs and milk in a small mixing bowl. Combine flour and salt then add to egg mixture and mix well. Cover and set aside for about 20 minutes.
Heat a lightly greased 20cm crepe pan or non-stick frying pan; pour 3 tablespoons of the crepe mixture into the centre of the pan. Lift and tilt pan to evenly coat bottom. Cook until top appears dry; turn and cook 15-20 seconds longer. Remove to a wire rack. Repeat with remaining batter, greasing pan as needed. When cool, stack crepes with greaseproof paper between.
Filling: In a small bowl combine the cheese sauce, Worcestershire sauce and nutmeg. Set aside.
Grease a baking dish and preheat the oven to 190 degrees C. In each crepe spoon 1 tablespoonful of sauce. Add asparagus spears then lay a piece of prosciutto over the top. Fold the crepes over and place seam side down in the baking dish. Drizzle the remaining cheese sauce over the top of the crepes then sprinkle with grated parmesan cheese.
Cover and bake in the preheated oven for 15 to 20 minutes or until sauce is nice and bubbly and asparagus is tender.