To make the cake: Lightly grease an 8-inch square or 9-inch round pan. Place the fruit in the pan, and sprinkle it with the lemon juice. In a medium-sized bowl, cream together the butter, sugar, baking powder, spice, and salt till smooth. Beat in the egg, then add the flour alternately with the milk (1/2 cup flour, the milk, remaining 1/2 cup flour), beating after each addition. Spoon the batter over the fruit in the pan, spreading it to mostly cover. To make the topping: Whisk together the sugar, cornstarch, salt, and spice. Sprinkle this mixture over the batter, then carefully pour the hot water over all. It will puddle on top; that's OK. Bake the cake in a preheated 375°F oven for about 60 minutes, until it's nicely browned on the top. Remove it from the oven, and serve warm with vanilla ice cream or whipped cream. Yield: 8 to 9 servings.