Preheat the oven to 180 C .
Place the butter and sugar in a bowl, and beat until light and creamy.
Add the vanilla and eggs and stir together well.
Sift in the flour, cocoa powder, baking powder and salt and mix until just combined
Fold in the chocolate.
Place large spoonfuls of cookie mixture on a greased and lined baking tray, allowing room for spreading.
Cook in batches for 15-20 minutes, until the bases are cooked.
Allow to cool on the tray or cooling rack.