Fresh asparagus risotto

Steam asparagus until crisp-tender (not too soft) and reserve cooking liquor. Cool asparagus, then cut into 2 cm lengths.
Bring stock (use 2 1/2 cubes to make it) and cooking liquor to a steady simmer in a large saucepan.
Heat oil and half the butter in a large, heavy-based pan. Add onion and sauté until glossy but not browned. Add asparagus and sauté for 1 to 2 minutes.
Add rice and stir to coat. Add hot stock, 125 ml (1/2 cup) at a time, stirring constantly and adding more stock as liquid is absorbed.
Continue until all liquid has been absorbed and risotto is porridge-like. (Rice should be tender but firm.) If you run out of stock before rice is tender, add warm water in the same way.
Season, remove from stove and stir in remaining butter and Parmesan cheese.
Serve immediately, with extra Parmesan and steamed asparagus spears, if desired.