It’s bold, real and wildly uncomfortable — the basic ingredients of a play created to spark debate. The Pulitzer- and Tony Award-winning Clybourne Park, playing at UW-Madison’s Mitchell Theatre through Nov. 24, starts on a chipper note, with characters blithely debating origins of ice cream while dropping subtle hints of cultural ignorance. But it erupts into poisonous verbal sparring and screaming matches about racism, prejudice and fear. It’s a heavy performance to watch, let alone perform.