Make the cake: Preheat oven to 325. Coat an 8-inch springform pan with cooking spray; dust with flour, tapping out excess. Place on a rimmed baking sheet. Spread apples in pan; set aside.
Whisk together flour, sugar, baking powder, salt, milk, oil, and eggs in a medium bowl until smooth. Pour over apples. Bake until set and pale golden brown, about 40 minutes.
Make the topping: Stir together butter, sugar, egg, and vanilla in a small bowl. Remove cake from oven, and pour topping over cake. Bake until golden brown, about 25 minutes. Let cool completely in pan on a wire rack. Remove sides of pan, and transfer cake to a serving plate. Serve slices drizzled with cream.