Preheat oven to 350F, grease three 6" round baking pans and dust with cocoa powder. Line bottoms with parchment.
Place all dry ingredients into the bowl of a stand mixer fitted with a paddle attachment. Stir to combine.
In a medium bowl whisk all wet ingredients (pour hot water in slowly as not to cook the eggs if very hot).
Add wet ingredients to dry and mix on medium for 2-3 mins. Batter will be very thin.
Pour evenly into prepared pans. I used a kitchen scale to ensure the batter is evenly distributed.
Bake until a cake tester comes out mostly clean. A total of 30-35mins.
Place sugar and water into a medium pot, stir to combine, but to not stir from this point forward. Cook over high heat, washing down the sides of the pot with a pastry brush dipped in water as needed to prevent crystals.
Cook until desired color of caramel is reached and immediately remove from heat. Very slowly, whisk in heavy cream. The mixture will bubble up (a lot) and boil. Add butter, return to heat, and bring back to a boil. Cook for 2 minutes whisking constantly.
Remove from heat and let cool to room temperature. Transfer to a container and place in fridge to thicken.*
Milk Chocolate Ganache:
Place chopped chocolate and cream into a microwave safe bowl. Stir to combine. Microwave for 20 seconds, stir. Microwave in 10 second intervals, stirring in between, until smooth and silky. Set aside to cool completely before using.*
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.**
Place bowl over a hot water bath on the stove and whisk constantly until the mixture is no longer grainy to the touch (approx. 3mins).
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.
Add cooled caramel and whip until smooth.***
Place one layer of cake on a cake stand or serving dish. Top with about 2/3 cup buttercream, drizzle with caramel and ganache and sprinkle with chopped pecans. Repeat with remaining layers. Crumb coat the outside and chill cake for 15mins. Frost and smooth the outside, chill for 30mins.
Using a teaspoon, drip ganache along the edges then fill in the top. Chill for 15mins.
Repeat with caramel and chill for 30mins.
If desired, top with rosettes and mini Turtles.****
* The ganache and caramel can be made the day before and left in the fridge overnight. Place plastic wrap directly onto the surface of each to prevent a skin from forming. ** Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. *** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. **** Adding rosettes and Turtles will cause the caramel to slide down more. I recommend skipping this step.