One of my favorite is Marilyn, with its large terracce on roof over the Cathedral Square ; next door, the fabulous Porte d'Annam of the famous French Chef Borloo on 22 Nha Tho St (facing the cathedral), not cheap but extraordinary food ; same owner : Madame Hien 15 Chan Cam (2 streets north of the Cathedral) but I prefer Porte d'Annam, in my opinion one of the very best in Hanoi