1. Preheat oven to 350°. Melt 6 tablespoons butter in a 10-inch cast iron or heavy ovenproof skillet over medium heat. Tilt skillet to coat sides. Remove from heat, and stir in 1 cup brown sugar. Arrange pineapple on bottom of skillet; set aside.
2. Stir together flour and next 5 ingredients in a large bowl. Set aside.
3. Melt remaining 6 tablespoons butter in a small saucepan. Remove from heat, and stir in 1/2 cup hot water, molasses, and remaining 1/2 cup brown sugar. Whisk in egg.
4. Add butter mixture gradually to flour mixture, stirring until well blended. Pour batter into prepared skillet.
5. Bake 35 to 40 minutes or until a toothpick inserted in center comes out almost clean. Cool in pan 10 minutes. Invert cake onto a round platter. Scrape any sugar mixture left in skillet over cake. Serve warm or at room temperature.