Sit the pineapple on its side and slice it in half, starting at the bottom and slicing all the way up through the leafy section. Chisel out the core of each half. Discard. Then cut around the fleshy sections with a knife (as you would a grapefruit). Remove flesh with a spoon and cut into small chunks. Reserve both the flesh and the rinds.
Melt butter in a saute pan over medium-high heat. Add pineapple chunks, but none of the juice, and stir occasionally for 5 minutes.
Sprinkle 1 tablespoon of sugar and stir occasionally for 30 seconds, or until it has dissolved. Repeat the same process, 1 tablespoon at a time, with the remaining sugar.
Pour in liqueur, let it heat up for 10 seconds, then ignite.