Whether on route to somewhere else, or a road trip destination in itself, a stop at Diesel and Creme is mandatory for us when in Barrydale.
Milkshakes are exceptional and the burgers, with a decent variety of options, are great. Even if you arrive hungry, wait to see if you have space before ordering a waffle to finish off!
Portions of everything are exceptionally generous, so my advice would be to consider sharing. That way you still get to enjoy all the different tastes, but can still walk out without waddling!