Heat oven to 350°F (175°C). Butter a 9-inch round cake pan and it with parchment. Pour caramel sauce into the pan and swirl to coat evenly. Arrange apple slices in a spiral or fan pattern over the caramel.
⅔ cup store-bought caramel sauce , 2-3 medium Honeycrisp apples
In a medium bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
1 ½ cups all-purpose flour, 1 ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon kosher salt, 2 teaspoon ground cinnamon, ½ teaspoon ground nutmeg
In a stand mixer or large bowl, cream butter and brown sugar until fluffy, 2–3 minutes.
½ cup unsalted butter , 1 cup light brown sugar
Beat in eggs one at a time, then stir in vanilla. With the mixer on low, add the dry ingredients in three additions, alternating with buttermilk in two additions, beginning and ending with the dry. Mix just until smooth.
2 large eggs, 1 teaspoon vanilla extract, 1 cup full fat buttermilk
Spread batter evenly over apples. Bake 40–45 minutes, or until a toothpick or cake tester inserted in the center comes out clean.
Let cake cool 20-30 minutes. Place a serving plate over the pan and carefully invert. Remove parchment if needed.
Drizzle with extra caramel before serving. Best enjoyed warm, especially with a scoop of vanilla ice cream.