21.   Bring mixture to a boil, then reduce heat to simmering and cook, stirring occasionally, until sauce has thickened.

22.   Bring to a boil, then reduce the heat and simmer until the sauce has thickened to your taste.

23.   Cook over low heat until sauce thickens.

24.   Continue to cook until the sauce thickens.

25.   Cook, stirring constantly, over low heat until sauce thickens.

26.   Cook over medium heat, stirring constantly, until sauce thickens.

27.   Cook until sauce thickens.

28.   Cook, stirring occasionally, until butter melts and sauce thickens.

29.   If necessary, turn heat to high until sauce thickens a bit.

30.   Increase the heat to high and continue cooking, stirring constantly, until the sauce has thickened and reduced somewhat.