Step 1Cut off the bottom 1 to 1 1/2 inches of the asparagus spears. Thinly slice the bottoms and add them to a large saucepan along with the trimmings from the minced onion. Shell the shrimp and add the shells to the saucepan. Cover with at least 5 cups of water or asparagus stock and bring to a boil. Reduce to a simmer and cook at least 30 minutes to make a mild stock.
Step 2Cut away the very tips of the asparagus. Chop the shrimp in one-half-inch pieces and add them to the asparagus tips. Slice the remaining parts of the asparagus in one-fourth-inch rounds.
Step 3Cook the asparagus rounds, 2 tablespoons butter and the onion in a large skillet over medium heat until the onion softens but does not turn color, about 5 minutes.
Step 4Add the rice and cook, stirring constantly, until all the kernels are opaque, about 3 minutes. Add the wine and stir until it evaporates. Ladle approximately 1 1/2 cups of the simmering stock through a strainer into the rice and cook, stirring, until it evaporates. When the bottom of the pan is almost dry, add an additional one-half to three-fourths cup and repeat.
Step 5Keep cooking this way, adding more stock as needed, until the rice begins to swell and become tender. Stir in 1 1/2 teaspoons of salt and the reserved chopped shrimp and asparagus tips, and continue cooking until the rice kernels are swollen and completely tender. Do not cook the mixture dry; the final texture should be somewhat soupy with slightly thickened liquid. This will take about 20 to 25 minutes in all.
Step 6Remove the skillet from the heat and add the remaining tablespoon of butter, the grated Parmigiano-Reggiano and the snipped chives. Vigorously stir these into the risotto. The liquid will thicken even more. Taste and add more salt if necessary. Spoon into hot shallow bowls and serve immediately.