1. Preheat the oven to 350°F / 175°C. Butter and line an 8" square pan with parchment paper.

Caramel Apple Layer

1. Wash, peel (optional) and thinly slice the apples.
2. In a small saucepan set over medium heat, melt the butter, brown sugar and salt together, stirring constantly until the mixture starts to simmer. Simmer for 2 minutes, then remove the mixture from the heat and pour into a 8" square pan.
3. Arrange the sliced apples on top of the caramel.

Vanilla Cake

1. In a small bowl, whisk together the flour, baking powder, and salt. Set aside.
2. In the bowl of a stand mixer fitted with the paddle attachment (or with a hand mixer, in a large bowl) beat together the butter and sugar for 3-4 minutes, until light and fluffy.
3. Use a rubber spatula to scrape down the sides of the bowl. Add in both eggs and the vanilla. Beat until well combined (~1 min.)
4. Add in half of the flour mixture, and mix by hand just until the flour is incorporated. Add in all of the milk and sour cream and mix until combined. Add in the rest of the flour, and lightly fold the mixture together just until all of the flour is incorporated.
5. Gently pour the cake batter into the prepared cake pan, smoothing out the top. Bake for 35-40 minutes, until a toothpick inserted in the center of the cake comes out clean or with only a few moist crumbs.
6. Let the cake sit in the pan for at least 20 minutes, then invert it onto a serving platter. Wait for the cake to mostly cool off before slicing, then enjoy!