Preheat your oven to 350°F (175°C) and prepare three 8-inch cake pans by lining the bottoms with parchment paper and greasing the sides.

In a large mixing bowl, sift together the all-purpose flour, granulated sugar, unsweetened cocoa powder, baking powder, baking soda, and fine salt.

In a separate bowl, whisk together the warm water, buttermilk, vegetable oil, eggs, and vanilla extract until fully integrated.

Gently fold the wet ingredients into the dry ingredients using a spatula, mixing just until combined.

Divide the batter evenly among the prepared cake pans and bake for 23-25 minutes.

Once baked, cool the layers in the pans for about 10 minutes, then transfer to the freezer for 30 minutes.

In a saucepan over medium heat, cook granulated sugar until it melts and turns amber. Stir in unsalted butter, heavy cream, and flaky sea salt until smooth.

In a mixing bowl, beat room temperature unsalted butter until creamy. Gradually add powdered sugar and heavy cream, then incorporate cooled caramel.

Place the first cake layer on your serving plate and spread caramel buttercream on top. Add the second layer and repeat.

After adding the third layer, create a ring of buttercream around the edges to hold in the caramel filling.

Chill the assembled cake in the freezer for 20 minutes or in the refrigerator for 30 minutes.

Frost the cake with chocolate buttercream and drizzle remaining salted caramel on top.