01 -
Preheat the oven to 175°C. Grease and flour a 23 x 33 cm rectangular baking pan.
02 -
In a large bowl, whisk together flour, sugar, cocoa powder, and baking soda. If using, add espresso powder. Set aside.
03 -
In another bowl, combine whole milk, mayonnaise, and vanilla extract. Mix until uniform and smooth.
04 -
Gradually incorporate the wet mixture into the dry ingredients. Stir until just combined; avoid overmixing.
05 -
Pour batter into prepared pan. Smooth the top. Bake for 30–35 minutes, or until a skewer inserted in the center emerges clean.
06 -
Remove from oven and set the pan on a wire rack. Allow cake to cool entirely before frosting.
07 -
In a medium bowl, beat softened butter until creamy. Add cocoa powder, vanilla extract, and salt. Gradually sift in powdered sugar, alternating with evaporated milk, and beat until light, fluffy, and spreadable.
08 -
Generously spread chocolate buttercream over cooled cake, creating thick, swirled patterns. Slice to serve.