Melt 4 tablespoons of butter in a small pot over medium heat. Once melted, add ½ cup of light brown sugar. Stir to combine. Cook over medium heat for 3 minutes, stirring occasionally, until the sugar dissolves and the mixture darkens slightly in color.

Turn the heat to low and add the apple pie spice, vanilla extract, and heavy cream. Whisk until smooth. Simmer for 1 minute. Add the crushed walnuts and stir until combined. Turn off the heat.

Pour the mixture into the prepared cake pan and smooth it into an even layer. Transfer to the refrigerator for 15 minutes.

Place the sliced apples in a bowl with 2 tablespoons of brown sugar, 1 tablespoon of cornstarch, and 1 teaspoon of cinnamon. Toss gently to combine. Set aside.

Sift ¾ cup of all-purpose flour, 1½ teaspoons of baking powder, 1 teaspoon of apple pie spice, and ¼ teaspoon of kosher salt into a small bowl. Set aside.

Add 4 tablespoons of butter and ½ cup of granulated sugar to a large bowl. Use an electric hand mixer to cream them together. Add 2 eggs and beat until smooth.

Add half the sifted dry ingredients and beat with the mixer until just combined. Add half the milk and beat until incorporated. Add the remaining dry ingredients and the remaining milk, along with 1 teaspoon vanilla extract. Beat until just combined. Don’t over-mix!

Remove the cake pan from the refrigerator. Arrange the apples in an even layer and press into the caramel. It’s okay if there is some overlap. Pour the batter over the apples and smooth it into an even layer.

Transfer the cake to the oven and bake for 50 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Let the cake stand at room temperature for 30 to 45 minutes. The cake should still be warm to the touch.

Place a large plate over the cake pan and carefully invert the cake onto the plate.

Slice the cake and serve warm with vanilla ice cream and a sprinkle of cinnamon on top. Enjoy!