Cut 0.5 cm off the ends and peel the white asparagus thoroughly. Bring a pan (large enough to hold the whole asparagus spears) of water to the boil and add a generous amount of salt. Cook the asparagus whole for 3–7 minutes, depending on thickness; pierce with a knife or cut off a piece – they should be just tender. Instead of boiling, the asparagus can also be fried in a large, heavy-based frying pan in olive oil until golden and tender on all sides; frying gives an extra intense flavour.
Put the butter in a saucepan and heat it until it sizzles and gives off a faint nutty aroma; add the sage leaves, turn down the heat, fry the sage leaves until they are just crispy, then remove the saucepan from the heat.
Finely grate the Parmigiano and toss three-quarters of the cheese into the warm asparagus on a serving dish; spoon the piping-hot sage butter over the top and sprinkle with the remaining Parmigiano and freshly ground pepper. Serve immediately.
