To make the apple brown betty: Preheat the oven to 350° F.
Butter a 9-inch-square baking dish. Sift the flour, salt, cinnamon, nutmeg, and sugar into a bowl. Cut the butter into small pieces; cut it into the flour mixture, using a pastry blender, until the mixture resembles coarse crumbs. Cut the bread into 1-inch-square pieces.
Soak the raisins in boiling water to cover for about 5 minutes, until plump, the drain them. Combine the bread, raisins, and sliced apples in a bowl. Sprinkle the bottom of the prepared baking dish with 3/4 cup of the flour mixture, add the apple mixture, and top with the remaining flour mixture. Bake, uncovered, in the preheated oven until the top of the brown betty is crisp and golden and the apples are tender, 35 to 45 minutes.
To make the rum whipped cream: In a chilled medium bowl, beat the cream and sugar until stiff. Beat in the rum.
Serve the betty warm, with the rum whipped cream.Makes 6