Preheat your oven to 350°F (175°C) and grease three 8-inch round cake pans. In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Mix in buttermilk, vegetable oil, eggs, vanilla extract, and hot coffee until smooth. Divide among pans and bake for 28–35 minutes.

Cool the cakes in their pans for 10 minutes before transferring to a wire rack to cool completely.

In a saucepan over low heat, combine sweetened condensed milk and heavy cream, stirring until it simmers. Remove from heat and stir in chocolate and unsalted butter until melted and smooth. Let cool at room temperature until thickened.

Beat butter in a medium mixing bowl until light and fluffy. Gradually sift in powdered sugar and cocoa powder, mixing well. Pour in heavy cream and vanilla extract, continuing to beat until smooth and airy.

Once the layers are cool, level the tops if needed. Place the first layer on a serving plate, spread fudge filling on top, add the second layer and repeat. Place the final layer on top and apply a crumb coat of buttercream around the cake.

Chill the cake in the refrigerator for 20–30 minutes to set the layer.

Frost the outer layer of the cake with the remaining buttercream, smoothing for an even finish. Create swirls or peaks if desired.

Heat heavy cream over low heat until it simmers. Pour it over chopped chocolate in a bowl, let sit for a minute, then stir until smooth. Let cool until slightly thickened before drizzling over the cake.

Get creative with toppings! Add brownie bites, fudge cubes, chocolate curls, or sprinkles. Slice and serve.