Is there such a thing as a single malt vodka?
I think you (and your friend) are confusing two similar terms.

&quot;Single Malt&quot; - the making of spirit from a single type of grain by a produced by a single distiller (for whisky, that's malted barley in the UK and malted rye in the US)
&quot;Single Barrel/Cask&quot; - the process of bottling each aged cask of liquor separately without mixing the casks together first.

&quot;Blended&quot; refers not to blending of the various casks from one batch together, but instead to blending together whiskys distilled by multiple distilleries or blending single malt with grain whisky. From the Wikipedia article on single malt:

To be called a single malt whisky in Scotland, a bottle may only contain whisky distilled from malted barley and produced at a single distillery. The regulations of other countries may allow malted rye.
If the bottle is the product of malt whiskies produced at more than one distillery, the whisky is called a blended malt or vatted malt, or pure malt. If a single malt is mixed with grain whisky, the result is a blended whisky. Single malts can be bottled by the distillery that produced them or by an independent bottler.

So, in the case of &quot;single malt vodka&quot;, that apparently means

“So what is meant by single malt vodka?” Elena queried.
“Most often, single malt vodka is 100% malted barley as the only ingredient.”

If you look at brands of vodka that call themselves this, this seems correct. Valt,  Franciacorta Single Malt Vodka, East Coast Single Malt Vodka, and several others list the sole ingredient as &quot;malted barley&quot;. Whether it's aged or not seems to depend on the maker.