Preheat oven to 400. Mix butter, mayo, dill, lemon juice, and parmesan into a paste. Place your salmon down on a lightly greased, foiled baking dish. Spread the mixture into a thin, even layer on top of your fish. Baking time will vary greatly with the thickness of your filet, but check for flaking after 10ish minutes. When this fish is just about done, turn your broiler to low and let it for for 30 seconds to a minute and a half until the mixture starts bubbly and getting some nice golden brown color. When it’s browned to your liking, remove and serve immediately.