Preheat the oven to 180°C/350°F, gas mark 4.
In a large bowl, beat the eggs and sugar together until smooth.
In a Tefal non-stick saucepan, melt the butter.
Take it off the heat and mix in the cocoa powder with a wooden spoon. Beat to remove any lumps.
Add the chocolate mixture to the eggs and mix thoroughly.
Stir in the vanilla essence.
Mix in the sieved flour a tablespoon at a time to prevent it going lumpy.
Mix in the chocolate drops and walnuts.
As this is a very sugary mixture, grease the inside of the Tefal 23 cm Square Baking Tin with margarine.
Bake at 180°C/350°F, gas mark 4 for about 25 minutes.
Remember to reduce the cooking time and temperature in a fan oven as they will cook much faster and easily burn.
Remove from the oven and leave to cool in the time. When cool, remove and cut into pieces.