viva_espana, My family is also from Galicia and we are also fans of Galician good-cooking. Our favorite "authentic" Galician restaurant in Madrid is Maceiras on C/Huertas,66. They have another location around the corner at C/Jesús,7.
I would recommend getting there before 9 pm to get a table. It gets quite crowded and stays crowded all night! The Caldo gallego is very good, the pimientos de Padrón are excellent,the Ribeiro and Albariño wines, the tabla de quesos gallegos,
queimada and filloas for dessert! If you get to go, I think you will be happy!