My bar top is actually ceramic tiles. I used two part apoxy to cover tiles to give the top a smoothe , glass like finish. It is probably 1/4″ thick. Some refer to it as “pour-on” I believe it is advertised now on this site. Look in the finishing ideas etc.. It’s expensive, I paid here in Canada $130 for a 1 Gal kit. Had to order from a paint store, Home Depot did not carry it.
If you use urethane etc.. make sure it’s UV resistant and resist yellowing over time. I used a water based type for easy cleaning and fast drying. I forget what name but think it was “Urethane ” brand ? I also used a gel type stain, a lot easier to use no mess at all. It was also the same brand.