Step 1: Preheat your oven to 350°F (175°C) and grease and flour two 8-inch round cake pans. Line the bottoms with parchment paper.
Step 2: In a large bowl, cream together the softened unsalted butter and granulated sugar until light and fluffy.
Step 3: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 4: In a separate bowl, whisk together the all-purpose flour, baking powder, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the cooled strong brewed coffee, beginning and ending with the dry ingredients. Mix until just combined, being careful not to overmix.
Step 6: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Step 7: Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
Step 8: For the buttercream, in a large bowl, beat the softened unsalted butter with an electric mixer until creamy and pale, about 2-3 minutes.
Step 9: Gradually add the powdered sugar, one cup at a time, beating until fully incorporated and fluffy.
Step 10: Pour in the cooled strong brewed coffee and vanilla extract. Beat on high speed for another 2-3 minutes until the buttercream is light, airy, and smooth.
Step 11: Once the cake layers are completely cool, place one layer on your serving plate or cake stand.
Step 12: Spread a generous layer of caramel coffee buttercream over the first cake layer. Drizzle about half of the 1/2 cup caramel sauce over the buttercream.
Step 13: Carefully place the second cake layer on top. Frost the top and sides of the cake with the remaining caramel coffee buttercream.
Step 14: For a decorative finish, warm the remaining caramel sauce slightly (if needed) and drizzle it over the top of the cake, allowing it to drip down the sides.
Step 15: Chill the cake for at least 30 minutes before slicing and serving to allow the buttercream to set.