Preheat oven to 350 degrees.
Rehydrate the cherries in the apple juice and let soak until tender. Drain and chop. Slice the pineapple as thin as possible. Sift together the flour, baking powder and salt, 3 times over parchment paper. In a heavy saucepan, heat 1 cup granulated sugar and cook until amber in color, about 5 minutes. Remove from heat and add 3 tablespoons of the butter. Mix carefully with a wooden spoon. Pour the caramel into a 10-inch cake pan and spread around the bottom. Sprinkle with brown sugar. Line the pan with overlapping pineapple slices, covering the entire pan. In the bowl of a mixer, cream together remaining 3 tablespoons butter and vanilla scrapings with remaining 1/4 cup granulated sugar. Add the eggs, 1 at a time, and mix until fluffy. Add the milk alternating in three additions with the sifted dry ingredients. Fold in the cherries. Transfer to the pineapple lined pan. Bake until a cake tester comes out clean, about 70 minutes. Invert onto a cake plate. While the caramel left in the bottom of the pan is still hot, quickly transfer it to a saucepot over low heat. Add heavy cream and stir to make a sauce. Let thicken and serve with cake.