1. Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.

2. In a large bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

3. Add milk, vegetable oil, eggs, and vanilla extract. Mix on medium speed for 2 minutes.

4. Stir in the boiling water slowly (the batter will be thin).

5. Divide the batter evenly between the prepared pans and bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

6. Remove the cakes from the oven and let them cool completely in the pans on a wire rack.

7. For the fudge frosting: In a small saucepan, heat the heavy cream until it begins to simmer. Pour over the chopped chocolate and butter in a bowl. Let stand for 5 minutes, then whisk until smooth.

8. For the salted caramel buttercream: Beat the softened butter until creamy. Gradually add the powdered sugar, then mix in the caramel sauce and sea salt. Adjust with heavy cream to achieve a smooth, spreadable consistency.

9. To assemble, place one cake layer on a serving plate, spread a generous layer of fudge frosting over it, then top with the second cake layer. Cover the entire cake with the salted caramel buttercream.

10. Decorate as desired and refrigerate for at least 30 minutes before serving for a cleaner slice.