Preheat oven to 375°F. Grease an 8-x8-inch square ovenproof baking dish with butter.
Peel pears carefully, making long full strokes with a vegetable peeler so that the pears hold their shape. Halve the pears and use a melon baller to core them. Rub lemon juice all of pears so they do not oxidize.
Fit pears snugly in prepared baking dish.
In a small bowl, using your fingers, combine brown sugar, cinnamon, and margarine until you have pea-sized crumbs. Sprinkle over pears and bake, covered with foil, for 30 minutes.
Using a slotted spoon, transfer pears to a serving plate. Pour cream into the hot baking dish, stirring to get up all the browned bits. Pour sauce over pears and serve.