This apple cake is super moist, perfectly sweet and packed with fall's most popular flavors. Apple is used in three ways -- applesauce is stirred into the batter, and fresh apple chunks are poked into the baked cake and then sprinkled on top of the frosted cake for flavor and crunch. Gooey caramel, a dusting of flaky sea salt and fluffy cinnamon buttercream are the irresistible finishes.
Preheat the oven to 350 degrees F. Spray a 9-by-13-inch baking dish with nonstick cooking spray.
For the cake: Whisk the applesauce, brown sugar, melted butter, sour cream, eggs and vanilla together in a large bowl until smooth. Add the flour, baking soda, cinnamon and kosher salt to the bowl and whisk until just combined. Pour into the prepared pan and smooth the top. Bake until golden brown and a toothpick inserted into the center comes out clean, about 1 hour. Leave the cake in the pan to cool completely, about 2 hours.
Once the cake is cool, use the handle of a wooden spoon to poke 25 holes in the cake (5 rows of 5 holes each). Press 2 to 3 apple pieces into each hole; reserve the remaining pieces for garnish. Pour and spread the caramel sauce over the cake and let it stand 10 minutes to sink into the holes and be absorbed by the cake. Sprinkle with the flaky salt.
Meanwhile, for the cinnamon buttercream: Beat the butter, confectioners' sugar, cinnamon and salt together in a large bowl with an electric mixer on medium-high speed until smooth. Add the cream and vanilla and continue beating until fluffy, 1 to 2 minutes. Dollop the frosting on top of the cake, then use a small offset spatula to spread it evenly. Garnish with the remaining apple chunks, a drizzle of caramel sauce and another sprinkle of flaky salt.
When measuring flour, we spoon it into a dry measuring cup and level off excess. Scooping directly from the bag compacts the flour, resulting in dry baked goods.