Preheat your oven to 180°C. Grease and line two 20cm round cake tins.

Start with the cake: sift the flour and cocoa powder into a large bowl, then add the sugar, butter, eggs, and milk. Beat until the mixture is smooth and well combined.

Divide the batter evenly between the prepared tins and smooth the tops. Bake for 25-30 minutes, or until a skewer inserted into the center comes out clean. Cool in the tins for 10 minutes before transferring to a wire rack to cool completely.

For the buttercream: beat the icing sugar with butter and vanilla extract until light and fluffy.

Once the cakes are cool, trim the tops to make them level if necessary. Place one cake layer on a serving plate or stand, and spread with a generous amount of buttercream. Top with the second cake layer.

Coat the outside of the cake with a thin layer of buttercream, then chill in the fridge for 20 minutes. This is your crumb coat.

Apply another layer of buttercream to the cake, smoothing it out for a clean finish.

Make the ganache by heating the cream in a saucepan over medium heat until it just starts to boil. Pour over the chocolate and let sit for 5 minutes, then stir until smooth and glossy.

Pour the ganache over the cake, letting it drip down the sides. Chill until set.

Use the fondant to create decorations inspired by Harry Potter, such as scarves in house colors, golden snitches, or the Hogwarts crest. Paint details with edible gold paint.

Arrange the decorations on and around the cake.