Melt together chocolate and butter and set aside to cool. In a medium size bowl, whisk together eggs, brown sugar, white sugar and vanilla (just until blended), don't overbeat. Add the melted butter and chocolate mixture. Blend slightly. Add sour cream and blend slightly again. In a small bowl, blend flour and baking powder. Add to the chocolate batter and blend slightly. Fold in chocolate chips. Pour into a 8x8-inch greased pan.
Bake at 350 degrees oven for about 25 to 30 minutes. Don't overbake; they should be slightly soft in the centre. They will firm up on cooling.