Grease and line a 20cm loose-bottomed cake tin with baking parchment. Preheat your oven to 180C / 350F.
Cream the butter and sugar together using electric whisks or a stand mixer until soft, then beat in the eggs.
Mix the flour, baking powder and bicarbonate of soda in a separate bowl.
Mix the milk and cocoa powder together, whisking as best possible. The cocoa powder will likely create a film and sit on top of the milk, but that’s fine.
Sift the flour mixture into the wet ingredients, then add the milky cocoa in. Using a rubber spatula, fold all the ingredients together until you get a smooth batter then spoon into the prepared tin. Bake for approximately 1 hour until a cake tested or skewer inserted into the centre of the cake comes out clean.
Remove from the oven and leave to cool for 10 minutes in the tin, before turning out to cool completely on a wire rack.
To make the chocolate fudge icing, mix the cocoa powder with the boiling water to make a smooth paste.
Cream the butter to soften it first, then sift in your icing sugar, beating it well until light, well combined and smooth. Add the cocoa paste, scraping down the sides of the bowl with a rubber spatula to ensure everything is incorporated. Whisk until your icing is uniform in colour and texture, and is smooth enough to spread.
Once the cake has cooled completely, use a sharp serrated knife to slice the cake widthways in half. Turn the cake half upside down so you have the smooth “bottom” on top, and the crumby inside facing downwards on your cake plate or stand. Add about a third of the frosting to the bottom half spreading it well to the edges.
Top with the second half of the cake, and spread the remaining buttercream over the top and sides of the cake.
Break up the chocolate flakes into big and small pieces, scattering them over the top of the cake and pressing lightly into the buttercream. Add the chocolate mini eggs and crème egg then slice and serve. Best eaten on the day of making.