Place chicken stock in a 2.5-qt. sauce pan and bring to a gentle simmer.
Preheat a 4-qt. chef's pan on medium heat until the rim of the pan is hot to the touch. Add the olive oil to the pan and allow to heat for 1 minute.
Add the diced onion and sauté until the onion is translucent, about 4 - 5 minutes.
Add the Arborio rice and sauté until the rice is coated with oil and has begun to turn opaque.
Add the white wine and stir with a wooden spoon until most of the wine is absorbed.
Add the warm chicken stock, one cup at a time. Stir continuously allowing stock to be absorbed before adding the next cup of stock.
After adding the fourth cup of stock, add the mascarpone cheese and asparagus. Continue stirring and adding the remaining stock one cup at a time. The rice should be creamy and al dente (total cooking time for rice is about 25 - 30 minutes).
Season with freshly ground pepper and sprinkle with freshly grated Parmigiano Reggiano. Serve immediately.