Heat oven to 350 degrees F. Spray two 9-inch round cake pans with baking spray (or grease with butter). Line bottoms of cake pans with parchment paper; spray paper with baking spray (or grease with butter).

In large bowl, whisk flour, baking powder, baking soda and salt until well combined. In separate large bowl or bowl of stand mixer with paddle attachment, beat butter and sugar on medium speed 1 to 2 minutes until pale and fluffy. Beat in vanilla, then beat in 1 egg at a time, scraping sides of bowl after each addition. Stir, then beat in buttermilk (mixture will look curdled). Add flour mixture in 3 batches, stirring each addition until just combined and occasionally scraping sides of bowl.

Divide batter evenly among prepared cake pans. Rap pans lightly on counter a few times to remove air bubbles. Bake 40 to 45 minutes until toothpick inserted in center comes out clean. Cool in pans 10 minutes, then carefully transfer to cooling rack to cool completely (remove parchment).*

To make the frosting: In large bowl or bowl of stand mixer with whisk attachment, beat butter until smooth. Stir in milk. Add 3 cups powdered sugar; stir, then beat until just combined. Stir in caramel sauce and salt. Add another 2 cups powdered sugar; stir, then beat until just combined. Beat in enough of remaining cup of powdered sugar as needed until frosting is smooth and spreadable but not drippy.

To assemble the cake: Using sharp serrated knife, carefully slice off domed tops of fully cooled cakes until flat. Use knife to cut cakes in half widthwise to create 4 thin cake layers. Place one bottom half of cake on serving plate or cake stand, cut side-up. Use offset spatula to frost top of cake layer with thin, even layer of frosting. Top frosted layer with top half of cake. Frost top of cake layer with thin, even layer of frosting. Top frosted layer with top half of second cake. Frost top of cake layer with thin, even layer of frosting. Top frosted layer with bottom half of second cake, cut side-down. Frost top and sides of cake with thin, even layer of frosting (make it really thin on the sides for that "naked look").

Cake can be stored, covered, at room temperature up to 3 days.

*NOTE: At this point, I like to wrap the cakes in plastic wrap and chill them in the fridge for a couple of hours or up to overnight so they are easier to slice and frost. This is optional, but highly recommended for cake decorating black thumbs like moi.