Preparation - Pierce the sweet potatoes with a fork. Place the potatoes in a microwave oven... arrange them on a paper towel, like spokes on a wheel. Microwave on full power for 12 to 14 minutes, or until the sweet potatoes are fork tender, stopping one time to turn the potatoes over, about halfway through. Let stand for about 10 minutes. Slice each sweet potato lenthwise. Scoop out the pulp leaving about a 1/4" shell. In a mixing bowl... mash the sweet potato pulp. Stir in the brown sugar, milk, and drained crushed pineapple. Spoon the mixture into the sweet potato skins. Arrange the filled sweet potato halves in a shallow microwave safe baking dish or plate. Place a dab of butter on top of each one. Cook on full power for about 3 to 4 minutes or until heated through.