You can take any 5 gallon recipe and just cut all of the ingredients in half to make 2.5 gallons.
I did a great SMaSH English Barleywine with just Marris Otter (to 1.100) and Goldings for bittering and for flavor. I fermented with a blend of US05 and Windsor (FG ~1.028) and aged on some french oak cubes. It is nice to go simple with a big beer because (in my experience) it leads to better aging than a beer loaded down with specialty malts.
I'd never do a barleywine as a single batch since a second runnings ESB is so easy and thrifty. How big is your mashtun and boil kettle?
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