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

In a large mixing bowl, combine flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk until well blended.

Add the eggs, milk, vegetable oil, and vanilla extract. Mix until just combined. Slowly pour in the boiling water and cooled brewed coffee; don't worry if the batter looks thin.

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

Once baked, let the cakes cool in the pans for about 10 minutes before transferring them to a wire rack to cool completely.

In a medium saucepan over medium heat, add the sugar and stir until it melts and turns golden brown.

Once the sugar is melted, whisk in the butter until melted. Pour in the heavy cream, whisking until smooth. Cook for another minute before removing from heat.

Stir in the sea salt gradually, tasting to see how salty you like it. Set aside to cool.

In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar and cocoa powder, mixing on low speed until well blended.

Pour in the heavy cream and vanilla extract, then beat on high until fluffy. Adjust cocoa powder to taste.

Place one cake layer on a serving plate. Drizzle some salted caramel sauce over the top, then add a layer of frosting.

Add the second layer of cake on top and repeat the caramel and frosting layers as desired.

Drizzle more salted caramel over the top of the frosted cake and sprinkle with sea salt.