Close to U Wittenberger Platz, the KaDeWe (Kaufhaus des Westens) is a famous luxury department store of West Berlin, its 6th and 7th floors are dedicated to food. The 6th floor is mainly food to shop, from all over the world, with a HUGE cheese section, quite dangerous for such a cheese lover like me! ^^ There’s also a French bakery, very expensive, but once in a while a nice treat.
On the 7th floor is a self-service restaurant, Le Buffet, under a glass roof. They have 2 nice breakfast offers for which you pay a certain price and can get a certain number of elements among a large choice, including hot drink(s). You can of course add other things from the buffet that you’ll pay extra to turn it into more like a brunch. It was really nice indeed.