Preheat oven to 350°. Place butter in a 12-in. cast-iron or ovenproof skillet. Place in oven until butter is melted, 4-5 minutes; carefully swirl to coat evenly. Sprinkle with pecans and brown sugar; drizzle with molasses. Arrange apple slices in a single layer over sugar, cut side down.
In a large bowl, cream butter and sugar until light and fluffy. Beat in egg, then molasses. In another bowl, whisk flour, baking soda, ginger, salt and cloves; gradually add to creamed mixture. Stir in hot water.
Pour over apples. Bake until a toothpick inserted in center comes out clean, 35-40 minutes. Cool 10 minutes before inverting onto a serving plate. Serve warm with applesauce, if desired.