Preheat oven to 275 degrees C. Grease moulds with additional butter. Melt butter and chocolate in a bowl, sitting in hot, but not boiling water.
In a separate bowl, mix cocoa powder and flour until well combined and lump free.
In another clean bowl, beat eggs and yolks with the sugar until light and foamy.
Carefully fold in the melted butter/chocolate and then the cocoa/flour mixtures. Try not to over mix, as this will release the air we just beat into the eggs/sugar. Pour mixture into the greased moulds (3/4 full only, as mixture will rise during baking) and bake for approximately 10-12 minutes.
Fondants should not be fully cooked, they should still be considerably liquid and soft in the centre. Remove and let cool slightly.
For the sauce:
Let the raspberries defrost together with the sugar.
Blend in electric mixture till well pureed.
Strain mixture with fine mesh to remove the seeds. (You can keep them in, if you like).
Remove chocolate fondants from the moulds, set on plate and serve with the raspberry sauce and vanilla ice cream.