Layered Apple Cake with Caramelized Apple Buttercream and Maple Walnut Crumble

For the apple cake

• Butter or nonstick cooking spray for the pans
• 2 1/2 cups all-purpose flour, plus more for the pans (625 ml)
• 1 1/2 tsp baking powder (7 ml)
• 1 tsp baking soda (5 ml)
• 1/2 tsp kosher salt, or fine sea salt (2 ml)
• 1/2 tsp ground cinnamon (2 ml)
• 1/2 tsp ground cardamom (2 ml)
• 3 large apples about 1 lb/454 g, preferably a crunchy variety such as Cortland, Honeycrisp, or Granny Smith
• 3/4 cup smooth tasting oil, such as canola, grapeseed, or extra-virgin olive oil (180 ml)
• 1 1/4 cups granulated sugar (375 ml)
• 2 tsp finely grated lemon zest (10 ml)
• 2 large eggs
• 1/2 cup buttermilk (125 ml)

For the caramelized apple buttercream

• 3 large apples about 1 lb/454 g, a crunchy variety such as Cortland, Honeycrisp, or Granny Smith
• 1/4 cup unsalted butter (60 ml)
• 1/4 cup granulated sugar (60 ml)
• 1/4 cup heavy cream (35% m.f.) (60 ml)
• 1 cup unsalted butter, room temperature (250 ml)
• 2 cups powdered sugar, sifted (500 ml)
• Pinch kosher salt or fine sea salt

For the apple topping

• 2 tbsp unsalted butter (30 ml)
• 2 tbsp granulated sugar (30 ml)
• 1 large apple a crunchy variety such as Cortland, Honeycrisp, or Granny Smith

For the maple walnut crumble

• 1 cup quick-cooking oats (250 ml)
• 1/2 cup coarsely chopped walnuts (125 ml)
• 1 tbsp unsalted butter (15 ml)
• 2 tbsp maple syrup (30 ml)
• 1/4 tsp freshly grated nutmeg (1 ml)
• Pinch kosher salt or fine sea salt

To serve

• Maple syrup optional, for drizzling

• 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.
• Sift together the flour, baking powder, baking soda, kosher salt, cinnamon, and cardamom into a medium bowl, and set aside.
• Peel and core the apples. Grate half of the apples, then finely dice the other half. Set aside.
• 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 until light and fluffy. Add the eggs one at a time, beating to incorporate fully after each addition. Scrape down the bowl as needed.
• With the mixer set to low speed, add the dry 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; do not overmix. Using a spatula, gently fold in the grated and diced apples until evenly distributed.
• Divide the batter evenly between the two prepared pans. Bake for approximately 25 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Allow the cakes to cool completely on a wire rack before carefully removing them from the pans.
• For the caramelized apple buttercream: Peel, core, and dice the apples. In a large skillet set over medium heat, melt the butter. Add the granulated sugar and whisk continuously until it dissolves and the mixture begins to bubble, about two minutes. Add the diced apples, and sauté, stirring occasionally, until they are very soft and beautifully caramelized, which should take about 10 minutes.
• Transfer the caramelized apples to a blender. Add the heavy cream and blend until you achieve a very smooth, thick puree. (Alternatively, you can use a stick blender directly in the skillet.) It is crucial to cool this apple puree completely before proceeding.
• Place the room temperature 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 about a minute to soften it. Add half of the sifted powdered sugar and beat on low speed until the sugar is moistened, then increase the speed to medium and beat until fully incorporated and fluffy. Add the **completely cooled** caramelized apple puree and beat until fully combined. Finally, add the remaining powdered sugar and the pinch of salt, beating on medium speed for several minutes until the buttercream is perfectly smooth, light, and fluffy. Set aside.
• For the apple topping: Line a baking sheet with parchment paper and set aside. Core the apple and slice it very thinly, preferably with a mandoline for evenness. I recommend keeping the skin on for visual appeal and added texture, but you can peel it if you prefer.
• In a large skillet set over medium heat, melt the butter. Add the granulated sugar and whisk until it is dissolved and the mixture is bubbly, about two minutes. Add the thinly sliced apples and cook until they are soft and slightly caramelized, about 5 minutes, flipping them halfway through. **Thin apple slices will soften quickly**, so pay close attention to ensure they remain intact. Using a firm, crispy apple variety (such as Cortland, Honeycrisp, or Granny Smith) is essential here, as softer varieties may fall apart.
• Gently remove the caramelized apple slices from the pan and arrange them flat on the prepared baking sheet, ensuring no slices overlap. Let them cool completely.
• For the maple walnut crumble: Heat a skillet over medium heat. Add the quick-cooking oats and coarsely chopped walnuts, and dry-roast them, stirring frequently, until they become fragrant and lightly browned, typically 5 to 8 minutes. Remove the skillet from the heat, then add the butter, maple syrup, freshly grated nutmeg, and a pinch of salt. Stir well to evenly coat the oats and walnuts. Return the skillet to medium heat and cook, stirring constantly, for an additional 3 to 5 minutes, or until the crumble becomes crispy and dry. Remove from the heat, then spread the crumble mixture out over a piece of parchment paper to cool completely.
• To assemble the cake: Once the cake layers are completely cool, use a serrated knife to carefully slice off the slightly domed tops of each cake to create flat, even surfaces (these delicious cake scraps are perfect for snacking!). Then, halve each cake horizontally to create a total of 4 even layers. Choose one of the bottom layers and carefully place it on a cake stand or your chosen serving plate.
• Spread approximately a quarter of the caramelized apple buttercream evenly over the first cake layer using a butter knife or an offset spatula. Carefully place the next cake layer on top and repeat the process two more times, alternating cake layers with buttercream, until you have stacked all four layers and used three-quarters of the buttercream. Frost the top of the cake with the remaining buttercream, smoothing it flat for a clean finish. Arrange the cooled caramelized apple slices artfully around the outside border of the cake, overlapping them slightly to create an elegant “fanned” effect.
• You can prepare the cake in advance up to this point: simply cover it with a cake dome, or loosely cover with plastic wrap, and refrigerate for up to three days. Remember to bring the cake back to room temperature at least an hour before serving to ensure the best flavor and texture.
• Right before serving, generously garnish the center of the cake with the cooled maple walnut crumble, creating an inviting mound. (Any remaining crumble can be served alongside the cake or enjoyed as a delightful breakfast topping!) If desired, drizzle with extra maple syrup just before serving. Serve immediately and enjoy!
• 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.

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