1 small onion
1 pound red beets with greens (about 3 medium)
4 cups water
1/2 stick (1/4 cup) unsalted butter
1 cup Arborio or long-grain rice
1/2 cup freshly grated Parmesan (about 1 1/2 ounces)
1 tablespoon bottled horseradish
Finely chop onion and trim stems close to tops of beets. Cut greens into 1/4-inch-wide slices and chop stems. Peel beets and cut into fine dice. In a small saucepan bring water to a simmer and keep at a bare simmer. In a 3-quart heavy saucepan cook onion in butter over moderate heat until softened. Add beets and stems and cook, stirring occasionally, 5 minutes. Stir in rice and cook, stirring constantly, 1 minute. Stir in 1 cup simmering water and cook, stirring constantly and keeping at a strong simmer, until absorbed. Continue cooking at a strong simmer and adding water, about 1/2 cup at a time, stirring constantly and letting each addition be absorbed before adding next. After 10 minutes, stir in greens and continue cooking and adding water, about 1/2 cup at a time, in same manner until rice is tender and creamy-looking but still al dente, about 8 minutes more. (There may be water left over.) Remove pan from heat and stir in Parmesan. Serve risotto topped with horseradish.