(Makes 4-6 servings, recipe adapted slightly from A Pinch of Salt Lake.)
Preheat oven to 375F. Bring large pot of water to a boil while you trim broccoli and cut into small flowerets. (I leave on a fair amount of the stem, but if stems are thick I recommend peeling some of the stem with a vegetable peeler.) When water starts to boil, put broccoli in and cook not more than 1-2 minutes (just until the broccoli turns bright green.) Immediately dump broccoli into a colander placed in the sink and let drain well.
Spray a low-sided glass or crockery casserole dish with non-stick spray or olive oil. (I used a pan that was 9″ X 13″, but next time I might one slightly bigger.) Put broccoli in casserole dish, spreading out into close to a single layer.
Stir together mayo, lemon juice, Dijon mustard and black pepper, then mix in finely chopped green onion and finely grated swiss cheese. Spread mayo-cheese mixture over the top of broccoli (I used a rubber scraper to do this. This is not a sauce that will completely cover the broccoli, but a thin layer of cheese sauce on the top.) Sprinkle parmesan cheese over mayo-cheese mixture. (On Thanksgiving Day, this could be made ahead up to this point and kept in the refrigerator. Let come to room temperature before baking.)
Bake uncovered for 20-25 minutes, until cheese is melted and slightly browned on top. (I baked mine for 22 minutes and it was nicely browned.) Serve hot.
This printable recipe from KalynsKitchen.com.