Step 1: Prepare the Cake Tins

• Preheat the oven: Set your oven to 180°C (160°C fan)/350°F/gas mark 4.
• Prepare the tins: Grease and line two 20cm round cake tins with baking parchment.

Step 2: Mix the Cake Batter

• Combine all ingredients: Place the self-raising flour, caster sugar, butter, baking powder, cocoa powder, eggs, milk, and vanilla extract (if using) into a large mixing bowl.
• Mix: Using an electric mixer, beat everything together for 2-3 minutes until smooth and fully combined. The batter should be light and fluffy.

Step 3: Bake the Cakes

• Divide the batter: Evenly divide the cake batter between the two prepared tins and smooth the tops with a spatula.
• Bake: Place the tins in the preheated oven and bake for 20-25 minutes, or until the cakes are risen and springy to the touch. A skewer inserted into the center should come out clean.
• Cool the cakes: Allow the cakes to cool in the tins for 5 minutes before turning them out onto a wire rack to cool completely.

Step 4: Make the Chocolate Icing

• Melt the chocolate and butter: In a heatproof bowl, melt the dark chocolate and butter together over a pan of simmering water or in the microwave. Stir until smooth.
• Add the golden syrup: Stir in the golden syrup to create a glossy, smooth icing.

Step 5: Assemble the Cake

• Spread the icing: Once the cakes are completely cooled, spread a layer of chocolate icing over the top of one cake.
• Layer the cakes: Place the second cake on top and spread the remaining icing over the top and sides of the cake.