Preheat the oven to 350°F. Line the bottom of a 9-inch springform pan, or regular cake pan, with parchment paper. Then grease just the sides of the pan.

In a small bowl, mix the brown sugar and cinnamon together. Spread in an even layer on the bottom of the pan. Then peel, core, and slice the apples. Toss them with lemon juice so they don't brown. Arrange the apples over the brown sugar layer in a pretty overlapping pattern. (See images if needed.)

Next, set out a large mixing bowl. Combine the granulated sugar and softened butter. Beat on high to cream the butter until light and fluffy, 2 to 3 minutes. Scrape the bowl with a spatula, then beat in the flour, baking powder, salt, eggs, milk, and vanilla. Scrape the bowl again and beat for just a few more seconds until perfectly smooth. Do not over mix the batter.

Spread the cake batter gently over the top of the sliced apples. Tap the pan on the counter to remove air bubbles. Then place the pan in the oven and bake for 40 to 50 minutes, until toothpick inserted in the center of the cake comes out clean.

Allow the cake to cool on the counter for at least 15 minutes. Then carefully flip the cake out of the pan onto a cake plate. Peel off the parchment paper.

For the whiskey sauce: Set a small sauce pot over medium heat. Add the heavy cream, brown sugar, butter, whiskey, and salt. Stir and heat until the brown sugar is fully dissolved and the sauce is smooth. Pour the whiskey sauce over the top of the cake. Serve immediately or cover and refrigerate until ready to serve. This cake is best served either warm or at room temperature.