Preheat oven to 180°C/160°C fan-forced. Grease two 20cm round cake pans and line base and sides with baking paper.

For the cakes, place milk, butter and instant coffee in a large saucepan and stir over medium heat until smooth. Remove from heat. Whisk in sugar until combined. Add eggs and whisk until combined. Add walnuts and stir until combined. Add flour and stir until just combined. Divide evenly between prepared pans. Bake for 25 minutes or until cooked when a skewer inserted in the centre comes out clean.

Stand cakes for 10 minutes in pan, then turn out onto a wire rack to cool completely. Meanwhile, make the syrup. Place sugar in a small saucepan with ¼ cup (60ml) water. Bring to the boil, stirring, until sugar dissolves. Add liqueur. Set aside to cool.

For the frosting, place butter in a stand mixer fitted with the whisk attachment and whisk on high speed for 5-6 minutes until pale and creamy, scraping down the side of the bowl with a spatula once or twice.

Reduce speed to low and, with motor running, slowly add the condensed milk. Bring the mixer back up to high speed and whisk for 2 minutes or until well combined. Place cakes on a board and level top with a serrated knife, if needed. Place 1 cake on a serving plate and brush with half the coffee syrup. Cover with some frosting and top with remaining cake. Brush cake with remaining syrup. Cover entire cake with a thin layer of frosting.

Chill for 20 minutes. Cover entire cake with remaining frosting until a uniform white colour. Chill for 20 minutes. Drizzle top with fudge and, using a brush or small offset spatula, blend and swirl fudge over the top and slightly down the sides, to mimic a Vietnamese coffee. Serve.