(Credit: Dario Acosta NY) German mezzo-soprano Tanja Ariane Baumgartner is one of the most sought-after opera singers of our time. Baumgartner has been a member of the ensemble at Oper Frankfurt since the 2009-10 season. During her time in Frankfurt, Tanja Baumgartner made appearances in numerous operas including “Carmen,” “Giulio Cesare in Egitto,” “Don Carlo,” “Medea,” “Die Frau ohne Schatten,” {…}