Heat the butter in a 9 - 10 inch straight-sided skillet. When it melts, add the olive oil and wait for it to come to temperature.
Add the diced onion, a sprinkle of salt and sauté 3 to 4 minutes without browning until the onions soften.
Add the rice, stirring with a wooden spoon to coat the rice. Heat without browning until the grains turn opaque.
Raise the heat, add the white wine and quickly evaporate.
Turn the heat back down, add enough warmed broth to cover the rice and cook slowly until the liquid evaporates. While the rice cooks, stir constantly, sometimes vigorously to release starches.
Repeat this operation of adding liquid and reducing until the risotto seems tender. Taste the broth as you go along and add salt judiciously to make the liquid flavorful.
When you think you are ready to add the last ladle of liquid, liquefy half a dozen asparagus spears in the water used to blanch the asparagus and finish the risotto with this liquid.
When the risotto is cooked to your liking, turn the heat off and let it rest for five minutes.
Spoon the risotto into flat bowls and garnish with whole asparagus stalks.
Sprinkle with Parmesan cheese and give a grinding of pepper before serving.