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 Celsius (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.