Spiced Sponge Cake

1. Preheat the oven to 165°C (325°F) and prepare three 15 cm (6-inch) round cake pans by greasing and lining only the bottom with parchment paper. 
2. In a medium bowl, mix and sift together the dry ingredients: flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg, and cardamom. 
3. In a separate large bowl or the bowl of a stand mixer fitted with the whisk attachment, beat the softened butter with the granulated sugar and light brown sugar for 2-3 minutes until smooth and creamy. 
4. Add the eggs and vanilla extract, and beat again for 3-5 minutes until the mixture is light, fluffy, and well-combined. 
5. Gradually add the dry ingredient mixture and buttermilk alternately in batches, mixing gently with a spatula between each addition, until the batter is smooth and lump-free. 
6. Divide the batter evenly among the prepared cake pans and bake in the preheated oven for 35-40 minutes or until golden brown and a toothpick inserted into the center comes out clean (check after 35 minutes; if not done, bake for an additional 5 minutes). 
7. Let the cakes cool in their pans for a few minutes, then carefully run a knife along the edges and remove them. Place the cakes upside down on a cooling rack to cool completely.  

Apple pie Filling

1. Cut the apples into pieces and mix them with lemon juice and cinnamon. 
2. In a large skillet or saucepan, melt the butter with the brown sugar and vanilla until combined. 
3. Add the apple pieces to the pan and cook over medium heat, stirring occasionally, until the apples are caramelized and tender. 
4. Let the apple filling cool completely.  

Streusel

1. Follow the Streusel recipe and let it cool completely.  

Mascarpone Whipped Cream

1. In a medium bowl, use an electric mixer to whip the cold mascarpone, heavy cream, powdered sugar, and vanilla for about 2-3 minutes until thick and spreadable.  

Mascarpone Frosting for Covering

1. Prepare the mascarpone frosting following the whipped mascarpone recipe and keep it chilled until ready to frost the cake.  

Assembling the Layer Cake

(Assemble the cake in a deep cake pan lined with parchment or using a tall, adjustable cake ring)  

1. Trim the tops of the cakes if needed using a cake leveler or a large serrated knife. 
2. Place the first cake layer in the pan or ring, add a layer of mascarpone whipped cream, apple filling, and a few streusel pieces. 
3. Add the second cake layer and repeat the process, finishing with the final layer of cake. 
4. Chill the assembled cake for about 30 minutes to 1 hour in the fridge, or for 15 minutes in the freezer. 
5. Cover the cake with a thin layer of mascarpone frosting and smooth it with a metal icing scraper. 
6. Let the cake rest in the fridge for 1 hour before decorating with streusel and apple pieces, and serve with salted caramel sauce.