Simmer the asparagus in boiling water till tender.
Drain carefully and lay the spears in a shallow, ovenproof dish.
Heat the oven to 200ºC/400ºF/Gas Mark 6.
Melt the butter in a shallow pan and fry the diced bacon in it till the fat is golden.
Tip the bacon and its cooking butter and juices over the asparagus, then sprinkle with the grated Parmesan.
Bake for 10 minutes till the cheese has melted.