Break the chocolate into small pieces and cut the butter into small cubes.
Place them in a heatproof bowl and set them over a pan of boiling water to melt, then remove from the heat and allow the mixture to cool.
In a separate bowl, sift together the flour, icing sugar, cocoa powder and baking powder.
Mix the eggs and the egg yolk with an electric mixer for about 1 minute until foamy, then add the melted chocolate and butter and mix well.
Fold in the dry ingredients.
Butter 6 ramekins and dust well with cocoa powder, then turn them upside-down and tap to remove the excess cocoa powder.
Divide the mixture between the 6 ramekins. Be careful not to fill the ramekins, ideally you want them only about half to 3 quarters full, otherwise they will rise too much and overflow.
Bake in the preheated oven at 200 degrees C (390 Fahrenheit) for 10 minutes or until firm on the outside but gooey on the inside.
Carefully remove from the oven, then run a knife around to ease up the edges. The top will be firm, but the middle nice and gooey.
Place a small plate on top of the ramekin and quickly turn it onto a plate.
Sprinkle some icing sugar on top and decorate with raspberries and mint.
Serve warm.