Good brownies must not be overcooked.
The secret is to take them out of the oven just before you think they are done - the middle should be soft and squidgy, not set firm. Don't worry if there is a dip in the middle and a crack on the top - this is how it should be - and you will find the mixture firms up on cooling.
Source: Good Housekeeping feature on Mary Berry, October 2016
