Preheat the oven to 160°C and grease and line a 16cm cake tin with baking paper. If you don’t have a small cake tin, you can make a single-layer cake using an 18cm or 20cm round tin.

Whisk the eggs until frothy, then whisk in the melted butter, sour cream and milk until combined. Add the cake mix and stir to form a smooth batter.

Pour the batter into the prepared cake tin and bake for 40-45 minutes or until cooked when tested with a skewer. Allow to cool completely before icing.

While the cake is baking, prepare the chocolate fudge frosting. Place the butter, chocolate, cream and vanilla in a small pot and gently heat while stirring until melted and smooth. Sift the cocoa powder and icing sugar together in a separate bowl, then gradually whisk into the melted chocolate mixture until smooth and dissolved. If your mixture looks a little lumpy, you can pass it through a sieve.

Pour the fudge icing mixture into a bowl and cover the surface directly with cling film. Chill for 1-2 hours or until it becomes a thick, spreadable consistency.

To assemble the cake, slice the cooled sponge in half horizontally to form two thinner layers and level off the top if necessary. Stack the cake with generous layers of fudge frosting and serve.

Tip: The addition of sour cream gives this cake a denser texture and subtle tang. If you don’t have any on hand, it can be substituted with 1/4 cup milk or buttermilk.

The fudge frosting will set firmly if chilled for too long. If it becomes too firm to use, gently heat it in the microwave in one or two 10-seconds bursts until softened. Be careful not to melt it!