In a 5- to 6-quart pan, bring 3 quarts water to a boil over high heat. Plunge broccoli rabe into water and cook until bright green, about 2 minutes. Drain and immerse in cold water. When cool, drain and coarsely chop.
In the same pan over medium-high heat, combine oil and onion. Stir often for 3 minutes. Add garlic and stir often until onion is limp, about 2 minutes. Add rice, stir, then add wine. Stir until wine evaporates, about 1 minute.
Add 4 cups broth and bring to a boil on high heat, stirring. Reduce heat to simmering and stir often until rice is tender to bite, about 15 minutes.
Stir in broccoli and, for a creamier risotto, a little more broth. Stir often until broccoli is warm, 2 to 3 minutes.
Stir cheese into risotto, then spoon into wide bowls.