There are many vegetables in Italian cooking with which, on occasion, one uses butter: green beans, zucchini, asparagus, spinach, Swiss chard, to name just the ones that come immediately to mind. When I was told that broccoli absolutely had to be cooked in olive oil, I bridled. Absolutely? Why? So here is a sauce where I pulled and stretched some regional borders to include something from the south—broccoli and mozzarella—and something from the north: butter and Parmesan. After all, if in t