Pre-heat the oven to 160C/320F. Grease and line a 9 inch spring form baking pan with non-stick baking paper
Place the butter and chocolate in a heatproof bowl and melt in the microwave in 30 second increments, stirring in between. You want all the chocolate to be melted and a smooth mixture. Set the chocolate aside to cool down
Add the remaining ingredients to a large mixing bowl and beat with electric beaters for 10 minutes. You want the mixture to triple in size and become pale, thick and fluffy. It may help to set a timer for 10 mins so you don't under beat the egg mixture
Slowly drizzle the chocolate mixture into the egg mixture while stirring with a spatula or wooden spoon. Then stir well to ensure the mixture is fully combined and none of the chocolate mixture has sunk to the bottom of the bowl
Pour the mixture into your prepared spring form pan and bake in the oven for 30 minutes
The cake should be firm on top when you take it out of the oven and a skewer should come out clean
Set on a baking rack to cool before removing from the baking pan. The cake will sink slightly in the middle as it cools, which is normal for flourless cakes
Serve with whipped cream and berries if desired. Best served warm
Video
Notes
NOTE THIS IS BASED ON THE INGREDIENTS WE USED, NUTRITIONAL INFORMATION MAY VERY DEPENDING ON THE INGREDIENTS USED.