Line a rectangular, non-stick cake tin / roasting tin (approx 28x20cm / 8x11 inches) with a large square of baking paper, snipping into the corners diagonally then pressing the paper into the tin so that both the base and sides are lined.
Put the dates and water in a saucepan. Bring the water to the boil, cover, turn the heat down to medium-low and simmer for 5 minutes, or until the dates have softened.
Add the chocolate, butter and sugar and stir until melted. Take the pan off the heat.
Sift the cocoa into a bowl, then mix in the flour and baking powder.
Add the chocolate mixture and the eggs to the bowl and stir to combine.
Pour the mixture into the prepared tin and spread it into an even layer.
Bake for 18-20 minutes, or until well risen and the centre is only just set.
Leave to cool in the tin for 15 minutes. Lift the cake out of the tin, remove the paper and cut it into 16 brownies.
It is best to store these brownies in an airtight container to keep them fresher for longer.Allow the brownies to cool completely before sealing them in the container and placing somewhere dark, dry and cool such as a kitchen cupboard or pantry.They will keep for up to a week.