Today i'm recommending Chez Franz cafe in Ixelles. It is by no means a lesbian or gay hang-out. BUT, it is almost guaranteed that you will find a few lesbians there at any time.
It is one of the hip places in Ixelles, near the upmarket Place Brugmann. It is open from early in the morning until late in the evening and you can eat, have a coffee, drink. It is famous for its brunches during the weekend and every sunday you can listen to live jazz music.
The food and the wine are not the best and it is not cheapest place around. But the atmosphere more than makes up for it.
Suitable for 30-40something crowd.
The address is 30 Avenue du Haut Pont, 1050 Brussels.
More information on its facebook page