Preheat the oven to 350°F (175°C). Grease two 8-inch round cake pans and line the bottoms with parchment paper.

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

In a separate bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla.

Add the wet ingredients to the dry ingredients and mix just until combined.

Stir in the hot coffee. The batter will be quite thin; this is normal.

Divide the batter evenly between the prepared pans and bake for 30–35 minutes, or until a tester inserted into the centre comes out with a few moist crumbs.

Let the cakes cool in the pans for 10–15 minutes. Turn them out onto wire racks, remove the parchment, and cool completely.

To make the chocolate buttercream, beat the softened butter with the paddle attachment for 3–5 minutes until pale, smooth, and fluffy.

Gradually add the icing sugar and cocoa powder, mixing on low speed until incorporated. Add the salt and vanilla, then add cream or milk 1 tablespoon at a time until the buttercream is smooth and spreadable. Mix on low speed for another 1–2 minutes to reduce air bubbles.

If necessary, trim the domed tops of both cake layers with a long serrated knife. Place the first layer cut-side up on a cake plate or board.

Pipe a ring of chocolate buttercream around the outer edge of the first layer to form a dam, then spread the salted caramel inside the dam.

Place the second cake layer cut-side down so the original flat pan bottom becomes the top of the cake.

Apply a thin crumb coat of chocolate buttercream and refrigerate for 20–30 minutes. Apply the final coat of buttercream and smooth the top and sides. Chill again until the buttercream is firm.

To make the ganache, place the semi-sweet chocolate in a heatproof bowl. Heat the cream until steaming but not boiling, then pour it over the chocolate. Let stand for 2 minutes and stir until smooth.

Allow the ganache to cool until thickened but still pourable. Spoon or pipe controlled drips around the edge of the chilled cake, then spread ganache over the top.

Pipe the remaining chocolate buttercream around the top and bottom edges as desired. Chill briefly to set before slicing.