Place butter in a broiler proof baking dish, approximately 6" in diameter. The cheese should NOT be sliced and should be in a single chunk.
Place cheese on butter and put under broiler for 5 to 7 minutes. Immediately after removing from broiler, place dish on a heat proof surface with nothing hanging overhead. Pour rum over the cheese and light it with a match.
Extinguish the flames after a few seconds by squeezing the lemon over it and serve while still very hot. Serve with bread OPA!