Before the jukebox musical, back when Mamma Mia!, Jersey Boys and Viva Forever! were still dollar-shaped glints in an as-yet-unborn producer’s eye, there was the pasticcio opera. Literally a musical ‘pastry’ or ‘pie’, these brought together arias from different operas, often by different composers, in a single work, designed as a way of feeding an 18th-century public whose appetite for opera was greater than composers’ ability to sate it with new music.