Pre-heat your oven to 160C Fan/400F/Gas Mark 6, line a swiss roll tin or a baking tray with a lip, with baking paper. The one I used was a Wilton tray that is 33.7 x 23.5 cm (13.25 x 9.25 inches)
For the sponge, whisk the eggs and sugar together with an electric hand whisk or in a stand mixer for 8 minutes until it reaches 'ribbon stage' - this is when you can drizzle some the mix into itself in a figure 8 and it doesn't sink back immediately
Gently fold in the flour and cocoa powder, folding gently and trying not to lose too much of the volume
Pour into the tin, and spread the mixture around using a palette knife. Bake for 12 minutes, if you lightly press it in the middle with your finger tip it should spring back
Remove from the oven and tip onto a clean sheet of baking paper. Remove the baking paper the sponge was baked with, then roll up the sponge, taking the clean baking paper with it, then leave to cool completely
Whip up the double cream for the filling with the icing sugar and vanilla extract
Gently unroll the sponge and spread the whipped cream all over it in an even layer, saving some for topping the swiss roll. Sprinkle over the crushed mini eggs. Re-roll the sponge and place onto your serving plate, trim the ends for a neater appearance
Drizzled the melted chocolate all over the swiss roll, pipe or dollop the reserved whipped cream along the top, and decorate with the whole and crushed mini eggs
Serve immediately, store any leftovers in the fridge for 2-3 days
Video
Notes
Make sure your ingredients are at room temperature before you start baking, particularly the eggs.
You need to roll up the swiss roll when it is hot from the oven. If it is too cold, it won't roll as neatly and could crack.
You can use any cocoa powder for this cake, of course the better quality it is, the better flavour it will have. Also do make sure you are using cocoa powder and not a hot chocolate powder.
I used Cadbury Mini Eggs, but any small chocolate eggs will work such as Smarties, Milkybar etc.
Although I provide cup measurements, I highly recommend weighing your ingredients out using digital kitchen scales. It is the most accurate way to measure ingredients and will ensure the best results. Digital scales are very low cost and can be purchased for around £12 ($16.50).
For teaspoon (tsp) and tablespoon (tbsp) measurements, please use measuring spoons and not the type of spoons you eat with. Again this will ensure accuracy and provide the best results.