Step 1

For the apple cake:  Place a rack in the middle of the oven and preheat to 350°F (175°C). Grease and flour 2 8-inch (20-cm) round cake pans, tapping out the excess flour, and set aside.

Step 2

Sift together the flour, baking powder, baking soda, kosher salt, cinnamon, and cardamom, and set aside.

Step 3

Peel and core the apples. Grate half of the apples, then finely dice the other half. Set aside.

Step 4

In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl if you’re using a hand mixer, beat the oil, sugar, and lemon zest on medium speed for 2 minutes. Add the eggs one at a time, beating to incorporate fully. Scrape down the bowl.

Step 5

With the mixer set to low speed, add the flour mixture in three batches, alternating with the buttermilk, beginning and ending with the flour mixture. Mix just until the last streaks of dry ingredients are combined. Using a spatula, fold in the grated and diced apples.

Step 6

Divide the batter between the prepared pans. Bake for about 25 minutes, or until a toothpick inserted in the center of the cakes comes out clean. Let the cakes cool completely on a wire rack before removing them from the pans.

Step 7

For the caramelized apple buttercream: Peel, core, and dice the apples. In a large skillet set over medium heat, melt the butter, then add the sugar and whisk until it is dissolved and the mixture is bubbly, about two minutes. Add the apples, and sauté until soft and caramelized, about 10 minutes.

Step 8

Transfer the caramelized apples to a blender. Add the heavy cream and blend to make a very smooth puree (you can also use a stick blender to do this.) Cool the puree completely.

Step 9

Place the butter in the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl, if using a hand mixer), and beat for a minute to soften. Add half the powdered sugar and beat on low speed to moisten the sugar, then increase the speed to incorporate fully. Add the cooled caramelized apple puree, and beat to incorporate fully. Add the remaining powdered sugar and the pinch of salt, and beat on medium speed until the buttercream is smooth and fluffy. Set aside.

Step 10

For the apple topping: Line a baking sheet with parchment paper and set aside. Core the apples and slice them very thinly (I like to keep the skin on, but you can peel them, if you prefer.)

Step 11

In a large skillet set over medium heat, melt the butter, then add the sugar and whisk until it is dissolved and the mixture is bubbly, about two minutes. Add the apples, and cook until soft and slightly caramelized, about 5 minutes, flipping them halfway through. Thin apple slices will soften quickly so you want to make sure to remove them from the heat while they still hold together. Using a firm, crispy apple (such as Cortland, Honeycrisp, or Granny Smith) is mandatory, as other varieties will fall apart.

Step 12

Gently remove the apple slices from the pan and set them flat on the prepared baking sheet, making sure no slices overlap. Let cool completely.

Step 13

For the maple walnut crumble: Heat a skillet over medium heat. Dry-roast the oats and walnuts, stirring from time to time, until fragrant and slightly browned, 5 to 8 minutes. Add the butter, maple syrup, nutmeg, and salt, and stir to evenly coat the oats. Cook, stirring constantly, for 3 to 5 minutes more, until the crumble crisps and dries up. Remove from the heat, then spread out the crumble mixture over a piece of parchment paper. Let cool completely.

Step 14

To assemble the cake: When the cakes are completely cool, cut off the pointy tops of each cake (keep the scraps to enjoy as a snack!), then halve them horizontally to create 4 even layers. Choose one of the bottom layers and set it on a cake stand or serving plate.

Step 15

Spread on a quarter of the buttercream with a butter knife or an offset spatula. Top with the next layer of cake and repeat two times more with the buttercream, ending with the fourth layer. Frost the top of the cake with the remaining buttercream, smoothing it flat. Arrange the caramelized apple slices around the outside border of the cake, overlapping them slightly to create a “fanned” effect.

Step 16

You can refrigerate the cake at this point: simply cover it with a cake dome, or loosely cover with plastic wrap, and refrigerate for up to three days. Make sure to bring it back to room temperature at least an hour before serving.

Step 17

Right before serving, garnish the center of the cake with a generous mound of maple walnut crumble. (Serve any remaining crumble alongside the cake, or enjoy it for breakfast!) Drizzle with maple syrup, if desired, and serve immediately.

Step 18

Recipe Credits: Apple cake and maple walnut crumble recipes adapted from Tessa Huff, Layered: Baking, Building, and Styling Spectacular Cakes. Caramelized apple buttercream recipe by Marie Asselin.