Because this place deserves all the publicity and custom it can manage, here’s my user review from Wales in Style:

I live in London and regularly eat at Michelin-starred places in the City, West End and throughout the South East. The food at Y Polyn is easily on a par with these restaurants, but the startling thing is that it manages to deliver this with a wonderful informality and easiness that is quite extraordinary. No fanciness here, just excellent food, in very pleasant surroundings, cooked by people who care about what their guests eat, not what they are wearing.

If you are within 50 miles, eat there. Book ahead.