Preheat oven to 350 degrees F.
Flour/grease and line bottom with parchment paper on (4) 7 inch cake pans.
Place all ingredients in mixing bowl.
Mix on low until all ingredients are wet.
Bring mixer to medium/high and mix for 2 minutes until completely combined.
Pour evenly into prepared pans and bake 28-33 minutes or until toothpick inserted comes out clean.
Let cool completely.
(this can be used for both buttercreams. I make each buttercream one at a time. First make the brown sugar buttercream for filling and crumb coat. Next make the pecan buttercream for the final coats and decorating.)
In large sauce pan add the egg whites and sugar (or brown sugar if making the brown sugar buttercream).
On low/medium heat you are going to whisk (continuously) egg mixture until sugar is completely dissolved (you can test it by rubbing a small amount between your fingers to test it, it should be completely smooth).
Transfer to mixing bowl and with whisk attachment whisk on high until stiff peaks form and mixture is completely cooled (if not completely cooled your butter will melt). If you have reached the stiff peak stage but meringue is still warm let it sit to cool to room temp.
Switch to paddle attachment.
On low speed add the butter one piece at a time.
Bring mixture up to high speed and continue to mix until well combined, smooth and creamy.
Add in the vanilla and salt, mix to combine.
For the pecan buttercream fold in the pecans by hand.
Cut tops of cakes if hump formed while baking.
Place first cake layer on cake board, secure it in place with a dab of frosting underneath.
Spread even layer of brown sugar buttercream on top of the cake layer, smooth with offset spatula.
(I left the outer edges of frosting higher to keep the caramel from slipping out).
Next add caramel on top of the buttercream arrange evenly, sprinkle with chopped pecans.
Repeat with the next two cake layers.
Add the top cake layer and crumb coat the cake with buttercream.
Refrigerate at least 30 minutes.
Put final coating of buttercream on cake using the pecan buttercream.
Pipe swirls on top and garnish with whole pecan halves and sprinkles.