One of the most feared critics in Italian opera is padding around her bedroom in a Milan retirement home, apologising for accepting visitors in stockinged feet. Luisa Mandelli, 95, moves nimbly, speaks fast and has crystal-clear memories of her days as a soprano, singing alongside Maria Callas in Giuseppe Verdi’s La traviata at La Scala in 1955.

“I challenge anyone to do 17 traviata recitals in a season like Callas could — she was the greatest, she governed her voice,” she recalls. For the past 16 years Mandelli has lived at Casa Verdi, the elegant and spacious home for retired and needy musicians built by Verdi before his death in 1901. But she is nowhere near retiring. Two or three times a week she rides…