Preheat oven to 180°C (350°F). Grease and line three 8-inch baking pans with parchment paper.
In a large bowl, whisk together flour, sifted cocoa powder, baking powder, baking soda, kosher salt, and granulated sugar.
Add eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients and mix until nearly combined.
Stir in the hot coffee until the batter is smooth and no lumps of flour remain.
Divide the batter evenly among the prepared pans and bake for 25–30 minutes, or until a toothpick inserted comes out clean.
Let the cakes cool completely before applying the frosting.
In a bowl, beat powdered sugar, butter, sifted cocoa powder, heavy cream, vanilla extract, and salt until smooth. Add caramel sauce and whip on high until fluffy.
Place a small amount of frosting on the serving surface. Set the first cake layer on top.
Pipe a frosting ring around the edge of the first layer, fill with frosting, and spread smooth. Fill the center with ⅓ cup caramel sauce. Repeat with remaining layers.
Frost the top and sides of the cake with remaining frosting. Slice and serve.
