Make the Caramel Sauce

1. Melt the butter in a large saucepan. Add the brown sugar, sweetened condensed milk, heavy cream and corn syrup and heat over medium heat, stirring constantly, until sugar is dissolved.
2. Turn the heat up to medium-high and heat, whisking constantly, until it comes to a full boil and reaches 215°F, about 4 minutes. When it reaches a full boil, it’s usually right about at 215°F. I recommend a candy thermometer, to be sure. Remove from heat and continue whisking until it stops boiling.
3. Pour into a bowl and refrigerate until at least room temperature, or until completely cooled.

Make the Cake Layers

1. Prepare three 8-inch cake pans with parchment paper circles in the bottom and grease the sides. Preheat oven to 350°F (176°C).
2. Combine the flour, baking powder, baking soda, cinnamon, nutmeg and salt in a medium sized bowl and set aside.
3. Add the butter, oil, brown sugar and vanilla extract to a large mixer bowl and beat together until light in color and fluffy, about 2-3 minutes. Do not skimp on the creaming time.
4. Add the eggs one at a time, mixing until mostly combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
5. Add half of the dry ingredients to the batter and mix until mostly combined.
6. Add the sour cream and applesauce and mix until well combined.
7. Add the remaining dry ingredients and mix until well combined and smooth. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Do not over mix the batter.
8. Gently fold the chopped apples into the batter until well dispersed.
9. Divide the batter evenly between the cakes pans and bake for 25-30 minutes, or until a toothpick comes out clean.
10. Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.

Make the Buttercream

1. To make the buttercream, beat the butter until smooth.
2. Add half of the powdered sugar and mix until well combined and smooth.
3. Add ¾ cup of the caramel sauce and mix until well combined and smooth.
4. Slowly add the remaining powdered sugar and mix until well combined and smooth. Add additional caramel sauce, as needed, to get the right consistency of frosting.
5. Beat the buttercream on high speed for 3-4 minutes with the paddle attachment to whip some air into it and add volume.

Build the Cake

1. To put the cake together, use a large serrated knife to remove the domes from the top of the cakes so that they’re flat. These cakes don’t really have much of a dome, but I like to make sure they’re completely flat.
2. Place the first cake on a serving plate or a cardboard cake round.
3. Spread about 1/2 a cup of buttercream evenly on top of the cake.
4. Pipe a dam of buttercream around the outer edge of the cake, on top of the layer of buttercream you just added. Fill the dam with about 1/2 a cup of caramel sauce and spread evenly. After filling the dam, level off any excess. You want the top of the dam to be even with the caramel sauce.
5. Add the second layer of cake and another layer of frosting, a dam and caramel sauce.
6. Top the cake with the remaining layer and frost the outside of the cake. Refer to my tutorial for frosting a smooth cake, if needed.
7. Use the remaining caramel sauce to add a drip to the sides of the cake and fill in the center, if desired. You may need to warm the sauce up just a bit, but don’t overheat it or it can separate. I used a spoon to drizzle it around the edges.
8. Use the remaining buttercream to pipe a border around the top edge of the cake. I used Ateco tip 847.
9. Store cake in an air-tight container or cake carrier in the fridge. Serve cool, but not really cold. Cake is best if eaten within 3-4 days.