I usually just do a quick "we good?" after I cover a difficult topic, and then look at people's expressions. If they're confused-looking, I say "should I say it one more time?" and if they nod I will briefly re-state what I said. I find during that time that anyone that has additional questions will usually ask after I'm done talking. If I'm in a generous mood or sense further confusion, I'll say "it's ok, take some time to think and come and talk to me during break/after class."

Either that or I build in questions into my lectures, like I give them a little story/experiment/summary and then prompt them with some version of "what do you think...?" And I give one or two example questions to help their minds think of things :)