Preheat the oven to gas 5, 180°C, 160°C fan. Cream the butter and caster sugar together until almost a whipped and creamy mixture is formed. Add the flour, cocoa and eggs and fold together then whisk again until creamy.
Lightly grease a 12-hole muffin tin and divide the mixture between them. Bake in the preheated oven for 20 mins until well risen and firm on top. Remove from the oven and allow to cool for 10 mins in the tin before using a small palette knife to ease each of the cakes out of the tin and onto a cooling rack to cool completely.
To make the buttercream, blend the butter and Trex in a bowl until creamy, then add the vanilla paste or essence, icing sugar and cocoa and mix carefully to avoid an icing sugar ‘cloud’, then beat until smooth and creamy
Spoon into a piping bag fitted with a star nozzle. Cut the cakes in half horizontally and pipe a layer of the buttercream onto the base layer, then top with the second layer. Pipe a rosette of icing on the top of the cake, starting close to the edges and ending in a peak on the top.
Now make the chocolate drizzle icing. Place the chocolate, butter and cream into a small heatproof bowl placed over a pan of gently simmering water and stir until melted, smooth and glossy. Remove from the heat and allow to cool for 10 mins. Place into a small piping bag and snip the end to form a thin point. Drizzle over the buttercream. Set aside to set while making the nests.
To make the nests, melt the chocolate in a heatproof bowl set over a pan of gently simmering water. Remove from the heat and add the broken Shredded Wheat and very gently stir into the chocolate to allow it to coat the wheat strands. Using small tea cups, place a tablespoonful of the mixture into each of the cups and shape into a nest shape, with a hollow centre, to resemble a nest. Chill for 10 mins, or freeze for 2-3 mins until set firm, then remove from the cups using a small palette knife. Place on top of each of the cakes, squishing down the icing peak to ‘glue’ the nest in place. Fill each of the nests with a few micro eggs and serve.