The key is not to overbake them. 25-30 minutes should be about right to get that lovely fudgy middle. Make sure you test the brownies with a skewer and if it comes out with few wet crumbs still on it, the time is up. However, if it comes out with wet batter on it, give it another 2-3 minutes and check again. Completely dry skewer will mean you baked your brownies for too long and they will most likely be a tad dry.