Peter Breu replies: The only really appropriate finish for this is a good quality marine spar varnish such as Epifanes. It needs to be many layers thick. I’d do at least five starting with very thin and ending with several layers that are thinned enough to flow out well.
Bob Couch replies: No varnish will really stand up to the use and abuse a countertop gets. The best choice in my opinion and experience is using plain mineral oil or a cutting board oil which has bees wax added. A coat should be applied once or twice a year to maintain the finish but yet if you sustain a burn mark or some other defect, it can be sanded and re-coated.
Elliot Savitzky replies: Tom McLaughlin recently replaced his wooden kitchen countertop and used epoxy for the finish. You can watch him at several stages on his Shop Night Live broadcast on YouTube. He has a video of the finished product on his website—epicwoodworking.com