Preheat oven to 400.
In a mixer, beat butter just to break up, not cream.
Add sugar and mix until lumpy.
Add chocolates and stir.
Add flour, cocoa, salt, baking powder to combine.
Mix eggs/yolk in a bowl and then add to mixer with vanilla to form dough.
Measure out 125 g. mounds and lay on parchment...not too tall or won't spread.
Bake for 15 mins. Centers will look slightly underdone but will set up as they sit.
Leave on tray at least an hour or 2 but can eat after 20 mins!