Melt dark chocolate in double-boiler; add butter and cook till it melt; allow to cool
Beat eggs in a bowl; add sugar and beat with electric beater
Add mint essence and chocolate mixture and mix with spoon
Fold in cocoa powder and flour
Grease cake pan with butter; pour brownie mixture in it.
Coat mint chocolate with flour and place on chocolate mixture; bake in a pre-heated oven at 180 C for 30 minutes; remove