Preheat oven to 350°F. Grease and flour two 9-inch round cake pans.
In a medium bowl, whisk flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, cream butter and sugar until light and fluffy. Beat in eggs, one at a time, then add vanilla.
Mix in the dry ingredients alternately with the coffee and sour cream, beginning and ending with dry ingredients.
Divide batter evenly between prepared pans and bake for 25–30 minutes, or until a toothpick comes out clean.
Let cakes cool completely before frosting.
For the buttercream: Beat butter until creamy. Gradually add powdered sugar.
In a small bowl, mix heavy cream with instant coffee until dissolved. Add to the buttercream along with ¼ cup caramel sauce. Beat until smooth.
Spread a layer of frosting over the first cake layer, drizzle some caramel, add the second layer, and frost the top and sides. Drizzle remaining caramel on top.