Clue: Performing twice in Tosca is stimulating for a soloist? (9)
Answer: ONANISTIC
Explanation: Definition: stimulating for a soloist
 **Anagram of**(Performing) [ **2 x**(twice) IN + TOSCA ].
As Woody Allen said, "… It's having sex with someone I love." And maybe also: "Having sex is like bridge. If you don't have a good partner, you'd better have a good hand."