Step 1: Prepare the Apples

1. Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan or springform pan.
2. Toss the apple slices with cinnamon and set aside.

Step 2: Make the Cake Batter

1. In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and cardamom.
2. In a separate large bowl, cream the butter and sugar together until light and fluffy.
3. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
4. Mix in the sour cream until smooth.
5. Gradually add the dry ingredients, mixing until just combined.

Step 3: Assemble and Bake

1. Pour half of the batter into the prepared cake pan.
2. Layer the cinnamon-coated apple slices on top.
3. Spread the remaining batter over the apples, smoothing it out evenly.
4. Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean.
5. Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack.

Step 4: Make the Caramel Sauce

1. In a saucepan over medium heat, melt the butter.
2. Stir in the brown sugar and heavy cream, whisking constantly until smooth.
3. Bring to a gentle simmer and let cook for 3-4 minutes, stirring frequently.
4. Remove from heat and stir in the salt and vanilla extract.

Step 5: Serve and Enjoy

1. Drizzle the warm caramel sauce over the cooled apple cake.
2. Slice and serve, optionally with whipped cream or vanilla ice cream.