Preheat your oven to 180°C (160°C fan/gas mark 4). Grease and line three 20cm round cake tins with parchment paper.

In a mixing bowl, combine cocoa powder with boiling water and chocolate stout, then set it aside to cool slightly.

In another large bowl, beat the unsalted butter, white caster sugar, brown sugar, and vanilla extract together until fluffy and pale, about 3-5 minutes.

Add in the eggs one at a time, mixing well after each addition, followed by the melted dark chocolate.

Gently fold in the flour and bicarbonate of soda alternately with the cooled stout mixture until fully combined.

Divide the batter evenly among the prepared cake tins and bake for 25-30 minutes until a skewer comes out clean.

Allow the cakes to cool in the tins for approximately 10 minutes, then transfer them to a wire rack to cool completely.

Whisk the egg whites and caster sugar over simmering water in a heatproof bowl, stirring until the sugar dissolves and the mixture is warm (about 2-3 minutes).

Remove from heat and beat with an electric mixer until stiff peaks form, about 5-7 minutes.

Gradually add in the softened unsalted butter and melted white chocolate, mixing until the buttercream is smooth and creamy.

Place one chocolate layer on a serving platter and spread a generous amount of Swiss meringue buttercream on top. Repeat with the second layer and place the final layer on top.

Cover the entire cake with a thin layer of buttercream and chill in the refrigerator for about 1 hour until firm.

Melt the white mini marshmallows in a microwave for about 20-30 seconds, then stretch them into thin strands and drape over the top of the cake.

Craft a spider from the black sugar paste and place it atop your Spider's Web Cake.