You simply follow the basic recipe for making a risotto in bianco, starting with a soffritto of onion or shallot sautéed in butter—and I think butter tastes best here—and proceed to add your rice, then a splash of white wine, then ladlefuls of broth, one by one, until the rice is almost done.
Then add some baby spinach, which you will have rinsed well of any grit and puréed in a blender with a bit of broth until perfectly smooth. Continue until the rice is done al dente, then proceed to the usual mantecatura, adding grated parmesan cheese and a dab of butter or—as I prefer—a slurp of heavy cream. The cream is not very orthodox, but I find that it complements the taste of the spinach very well.
Serve immediately, with additional cheese on the side for those who want to top their risotto with it.