Chop four Rocher chocolates into small pieces, as well as the bittersweet chocolate. Place the butter into a bowl with all of the chocolate pieces, and let the ingredients melt together over a pot of hot water.
Remove the bowl from heat and add the flour, eggs, sugar, and baking powder. Mix well to form a smooth batter.
Pour the batter into a baking pan and press the remaining Rocher chocolates on top. Finally, bake for 25 minutes at 350 °F.