1 pound asparagus, peeled, trimmed and cut into one-inch-long pieces, tips reserved
5 to 6 cups vegetable stock
2 tablespoons extra virgin olive oil
3 tablespoons unsalted butter
1/3 medium red onion, diced
1 1/2 cups Arborio rice, or Carnaroli
1/2 cup dry white wine
Salt to taste
1/2 cup grated Parmigiano Reggiano
Bring a pot of water to a boil. Add half the asparagus stalks and cook until soft, about 5 minutes. Rinse quickly under cold water. Put cooked asparagus in a blender or food processor and add just enough water to allow machine to puree until smooth. Set aside.
Heat the stock in a medium saucepan over low heat. Put oil and 1 tablespoon butter in a large, deep nonstick skillet over medium heat. When it is hot, add onion, stirring occasionally until soft but not yet brown, 3 to 5 minutes.
Add rice and cook, stirring occasionally, until it is glossy, about 2 to 3 minutes. Add white wine, stir, and let liquid bubble away. Add a large pinch of salt. Add warmed stock, 1/2 cup or so at a time, stirring occasionally. Each time stock has just about evaporated, add more.
After about 15 minutes, add remaining asparagus pieces and tips, continuing to add stock when necessary. In 5 minutes, begin tasting rice. You want it to be tender but with a bit of crunch; it could take as long as 25 minutes total to reach this stage. When it does, stir in 1/2 cup asparagus purée. Remove skillet from heat, add remaining butter and stir briskly. Add Parmesan and stir briskly, then taste and adjust seasoning. Risotto should be slightly soupy. Serve immediately.