1. Preheat oven to 425F.
2. Heat butter in a 10-inch well seasoned cast iron skillet over medium heat, until foam surrenders, then stir in sugar (sugar will not dissolve).
3. Arrange pears in skillet with cut sides up. Add cognac and let alcohol evaporate.
4. Sprinkle pears with cinnamon and ginger.
5. Add raisins and let cook undisturbed until sugar turns golden caramel.
6. Place oven rack in the middle position. Place pastry dough over the caramelized pears, tucking edge around pears. Bake tart until pastry is golden brown, about 35 minutes.
7. Let cool for 5-7 minutes. Either invert tart or serve straight from skillet.
8. Serve warm or at room temperature with ice cream, whipped cream, or both!