Pre-heat the oven to 177 C (350 F) and grease with butter a 9 or 8 inch square pan. Mix the sugar with the butter. Put the eggs in a large bowl and mix them with the sugar and the butter. Then, pour in the vanilla, the cocoa, flour, salt and baking powder into the same bowl where you have the sugar and butter. Mix everything very well and make sure to get rid of all the crumbs. Then pure the mixture into the baking pan and on the top put the little chocolate squares. Finally, bake for 35 minutes.