We hid shredded apple in the cake for extra flavor and moistness, but the real star here is the gorgeous array of fall fruit, glazed with bourbon-infused caramel.
Preheat oven to 350°. Grease a 9-inch round baking pan.
For caramel: In a small saucepan, melt 2 tablespoons of the butter over medium heat. Whisk in 1/2 cup brown sugar and 2 tablespoons of the bourbon. Bring mixture to a boil. Boil, uncovered, stirring constantly, for 1 minute. Remove from heat; let cool slightly. Pour into a prepared pan, spreading evenly. Arrange apple slices over caramel, overlapping slightly, if desired
In a medium bowl, stir together all-purpose flour, rye flour, baking powder and salt.
In a large bowl, using an electric mixer on medium speed, beat the remaining 6 tablespoons softened butter for 30 seconds. Add the remaining 1/2 cup brown sugar and beat until well combined. Add egg, remaining 2 tablespoons bourbon, and the vanilla. Beat until combined. Beat in shredded apple. Beat in half of the flour mixture at a time just until combined.
Drop batter in spoonfuls over apple slices in pan and spread gently and evenly to edges. Bake 40 minutes or until a toothpick inserted near center comes out clean. Cool on rack 10 minutes. Loosen cake from sides of pan. Invert onto a serving plate. Serve warm.