Add the arborio rice and toast it in the pan, stirring constantly, for 2-3 minutes. Add the wine and cook until all the liquid is absorbed, about 1 minute. Ladle about half of the stock or broth into the pan with the rice and bring it up to a bubble, stirring constantly. Simmer the mixture, stirring frequently, until all the liquid is absorbed, 4-5 minutes. Ladle in about half of the remaining liquid and continue stirring the rice until that liquid has fully absorbed, 4-5 minutes. Ladle in the remaining stock and cook the risotto until most of the remaining liquid has been absorbed and the rice is al dente, about 7 minutes. Season the risotto with salt and freshly ground black pepper.
Once you get the risotto going, place another skillet over medium-high heat with the remaining tablespoons of butter and EVOO. Add the mushrooms and cracked clove of garlic into the other pan and cook, stirring occasionally, until the mushrooms are golden brown and tender, about 10 minutes. Season with salt and freshly ground pepper, and add the balsamic. Cook about 1 minute to glaze the mushrooms then remove from heat and discard the garlic clove. Keep the mushrooms warm until the risotto is finished.
Once the risotto and mushrooms have finished cooking, add the spinach puree and remaining 1/2 cup of Parmigiano-Reggiano to the risotto and give it a good stir. Spoon the risotto out onto a serving dish and top it with the glazed mushrooms. Pass additional Parmigiano-Reggiano at the table.