Preheat the oven to 350°F. Line two 8-inch cake pans with parchment paper and spray with non-stick spray; set aside. In a mixer bowl, whisk together the butter and sugar until combined. Add the eggs and vanilla extract, whisking until smooth. In a separate bowl, combine the buttermilk and coffee, whisking until fully blended. In another bowl, sift together the flour, baking powder, and salt. Alternately add the buttermilk mixture and the flour mixture to the butter mixture, stirring until no lumps remain.

Evenly divide the batter between the prepared cake pans. Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean. Remove the cake layers from the pans and cool them on a wire rack. Once completely cooled, use a serrated knife to level the tops and slice each layer in half.

To prepare the frosting, place the softened butter in a mixer bowl and whisk on high speed, scraping down the sides regularly, until the butter is light, fluffy, and pale in color. Add the dulce de leche and Kahlúa (if using), then whisk again until the buttercream is fluffy. For a lighter texture, add 1 to 2 cups of confectioners’ sugar and whisk for an additional 3 to 4 minutes. Reserve ¾ cup of the frosting and transfer it into a pastry bag fitted with a star tip.

To assemble the cake, lightly soak each cake layer with Kahlúa or coffee using a spoon or dispenser bottle. Spread a thin layer of frosting between each layer as well as on the sides and top of the cake. Smooth the frosting with a flat spatula. Refrigerate the cake for 20 to 30 minutes to set.

While the cake chills, prepare the chocolate ganache: heat the cream in a small saucepan until it’s nearly simmering, being careful not to burn it. Remove from heat and whisk in the semi-sweet chocolate until melted and slightly thickened. Allow the ganache to cool for about 5 minutes so it thickens and air bubbles dissipate. Pour half of the ganache into a disposable pastry bag or a ziplock bag.

Use the ganache to decorate the sides of the cake by piping it from the pastry bag. Pour the remaining ganache over the top and smooth it with a spatula. Return the cake to the refrigerator for another 20 to 30 minutes to set.

If desired, once the ganache is set, pipe the reserved frosting on top for decoration. You can also garnish with coffee caramel macarons for an elegant finish. Keep the cake refrigerated until ready to serve.

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