Preheat your oven to 325 degrees F. Spray three 8-inch cake pans (or four 6-inch pans) with nonstick spray, line the bottom with parchment paper and spray again. Set aside.
In a medium sized mixing bowl, combine the flour, baking powder and salt. Whisk to combine and then set aside.
In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and the sugar. Mix on medium-high speed for about 3 to 5 minutes, until the mixture is light and fluffy.
Add the eggs, one at a time, scraping down the sides and bottom of the bowl to make sure all of the butter and sugar are mixed well with the eggs. Add the vanilla.
With the mixer on medium-high speed, add the dulce de leche and mix for a couple minutes. The mixture will get a little lighter in color.
With the mixer on low speed, alternately add the dry ingredients and the milk, starting and ending with the dry mixture. Mix until just combined.
Fold in the honeycomb pieces. NOTE: the honeycomb will cook and create caramelized areas and 'craters' in the cake. Don't worry, any holes will get filled with buttercream and you'll have these delicious bites of salted caramel crunch.
Pour the batter into your three 8-inch pans (or four 6-inch pans) and bake until a toothpick inserted in the center of the cake comes out with a few moist crumbs on it, about 30 to 35 minutes.
Allow the cakes to cool in the pan on wire racks for about 10 to 15 minutes and then invert onto wire racks and allow to cool completely.
Cakes can be made ahead of time and wrapped in plastic wrap and frozen until ready to use. Be sure to give the cakes about 30 to 60 minutes at room temperature before stacking and decorating.
Mix sugar, water and corn syrup in a small saucepan.
Bring the water and sugar mixture to boil over medium heat, but DO NOT STIR. Let the mixture cook until it caramelizes into a golden brown color.
Remove the caramelized sugar syrup from the heat and slowly mix in the cream. Pour in just a tiny bit at a time, especially at the beginning, and mix to combine.
Mix in salt and vanilla. Stir to combine.
Set the caramel sauce to the side and let cool completely before making the frosting.
Once the caramel sauce is cooled completely, divide it in half and reserve one half of the caramel drizzle in the cake. Use the other half for the frosting.
In a stand mixer fitted with the paddle attachment, combine the butter, powdered sugar and caramel together and beat until smooth. If the icing seems to stiff, add a bit of cream until it reaches a smooth, spreadable consistency.
Place the first cake layer in the center of the cake board. Spread about 1 cup of the buttercream evenly across the cake layer. Drizzle with about a couple tablespoons of caramel sauce. Sprinkle the honeycomb over the caramel and buttercream.
Place the second cake layer on top of the filling and repeat these steps. Place the third cake layer, top side down.
Crumb coat the entire cake with a thin layer of frosting and freeze for about 10 to 15 minutes to set.
Once the crumb coat is set, continue to frost the cake with the remaining buttercream, and then use the remaining caramel sauce as a drip. Top with honeycomb.
