Cut off top, bottom and outer skin of pineapple. Turn remaining pineapple on its side and slice into 1/2-inch thick rounds. Select the prettiest 4 rounds. Using a small round cookie cutter or pairing knife, cut out and discard the core.
Place sugar on a small plate.
Take a ring of pineapple and dip both sides in butter. Dredge pineapple in sugar and place on a cookie sheet. Repeat with 3 more rings. Save remaining slices for tomorrow's breakfast.
Bake rings for approximately 15 minutes, or until they brown and caramelize.
Let pineapple cool, then place rings on individual plates, browned bottom side up. Place a scoop of sorbet in the center of the ring. Using a small spoon, make an indentation in the top of the scoop of sorbet and fill the indentation with grenadine to the point that it drizzles down the side of the sorbet scoop.