1. Preheat the oven to 180 ̊C, gas mark 4. Put the butter and sugars in a bowl and, using electric beaters, beat for 3-4 minutes, until light and fluffy. Beat in the eggs, one at a time, followed by the vanilla extract.
2. In a separate bowl, mix the flour, baking powder, bicarbonate of soda and salt. Tip into the butter mixture, beat until just combined, then stir through the chocolate chunks. Tip into a 20cm ovenproof frying pan (or shallow cake tin) and bake for 25-30 minutes, until golden (25 minutes yields a molten centre, 30 minutes will be slightly more set).
3. Cool for 5 minutes, then top with vanilla ice cream before serving, if liked.