This super moist three layer cake is filled with autumn spices and grated apples! It's topped with brown sugar buttercream and apple cider bourbon caramel!
Begin by making the cake. Preheat oven to 350℉. Butter and flour three 9-inch round cake pans. Line the bottoms of the pans with parchment paper as well.
In a medium bowl, whisk together flour, baking soda, baking powder, cinnamon, ginger, allspice, nutmeg, and salt. Set aside. In a large bowl, whisk together the brown sugar, eggs, vanilla, milk, and canola oil until smooth. Add the flour mixture and stir until combined. Fold in the grated apples and stir until just combined. Divide the batter among prepared pans and smooth out the tops with a rubber spatula.
Bake for 22-25 minutes, or until a toothpick inserted into the cake comes out clean. Cool cakes in pans for 20 minutes, then cool for the rest of the way on a wire cooling rack.
Next, make the caramel. In a medium saucepan, bring the sugar, apple cider and corn syrup to a boil over high heat. Cook until the sugar is dissolved, but DO NOT stir! Swirl the pan on the stove if you need to. Continue cooking, without stirring, until an amber caramel forms, about 6-7 minutes. Remove from the heat and carefully stir in the cream. Let cool for 1 minute, then stir in the bourbon. Bring the mixture to a boil over medium-high heat and cook, stirring, for 1-2 minutes. Stir in the salt. Let the caramel sauce cool. (I made mine the night before but this isn't crucial. Stick it in the fridge if you have to!)
Make buttercream. In a heatproof bowl, whisk together the brown sugar, egg whites, vanilla, and salt until smooth and combined. Place bowl over a pan of boiling water, (make sure the bottom of the bowl doesn't touch the water!), and cook until sugar has dissolved, 3-4 minutes. Remove from heat. Pour mixture into the bowl of an electric mixer and beat on medium speed for 10-12 minutes, until mixture is lighter in color and fluffy. Increase the speed to high and beat until stiff peaks form, another couple of minutes. Reduce speed to medium-low and gradually add the butter, 2-3 tablespoons at a time, and beat until smooth. If the mixture seems to have separated after all the butter is incorporated, beat on medium-high until smooth. Then, reduce speed to low, and beat for 3 more minutes.
To assemble the cake, place one layer on a serving plate, and spread the top with buttercream. Top with another layer and spread top with buttercream. Top with the third layer and spread with another layer of buttercream, leaving a little bit left for the sides of the cake. Use the leftover buttercream to "half" frost the sides, to create a "semi-naked" effect. Use an offset spatula or bench scraper to smooth out the sides of the cake. Pour the caramel over the cake and let it drip down the sides (you won't use it all, just use your desired amount!). Garnish with mini apples and flowers, if desired.