Preheat your oven to 350°F (175°C) and grease three 9-inch round cake pans. In a bowl, whisk together flour, baking powder, baking soda, and salt. Cream butter and sugar together for 3-5 minutes, then add eggs one at a time followed by vanilla. Alternate adding dry mixture with buttermilk and coffee, starting and ending with dry ingredients. Divide the batter between pans and bake for 25-30 minutes.

While the cakes bake, prepare the caramel sauce by melting sugar in a saucepan over medium heat until golden amber. Add butter until combined, then gradually pour in heavy cream while stirring. Stir in vanilla extract and a pinch of salt.

Once cakes are cooled, whip the butter for frosting until creamy. Slowly mix in powdered sugar, then add heavy cream and cooled caramel sauce, mixing until fluffy.

Assemble the cake by layering the cake with frosting between each layer and covering the top and sides with the remaining frosting.

Drizzle remaining caramel sauce over the top of the cake and optionally add a sprinkle of sea salt for contrast.

Let the cake set for 30 minutes at room temperature to meld flavors, then slice and serve with coffee or tea.