For the cake: Preheat oven to 350 degrees F. Grease 2 9-inch cake pans.
Sift flour, cocoa powder, baking soda, and salt into a mixing bowl; set aside. In a separate bowl, whisk sugar and eggs until light and aerated. Stir in melted chocolate, vegetable oil, buttermilk, and coffee and whisk until combined.
In three additions, pour wet mixture into dry mixture, whisking well after each addition. Pour batter into prepared pans and bake 45 minutes to 1 hour, or until a wooden toothpick inserted in the center comes out clean. Let cakes cool.
For the frosting: Beat cream to soft peaks. Set aside. Beat together dulce de leche, cream cheese, vanilla and salt in a stand mixer fitted with the paddle attachment until well combined. Fold in the whipped cream, cover with plastic wrap and keep room temperature until ready to use.
To assemble the cake: Once the cake is completely cool, put one layer on a serving plate and put a healthy dollop of frosting on top. Spread the frosting to the edge then place the other cake layer on top and frost.