I have never used a single portafilter (just thrown out the extra shot when only one is needed), but I completely understand the want to conserve beans. The shop I'm working at now has a single that doesn't fit my tamper ( bought a tamper to use at the shop, which works perfectly for the double baskets) To use the single, I'd have to use the plastic tampers attached to the grinders that everyone else uses, but I can't stand. SOOO, to finally get to my question. Is there a legitimate way to pour the equivalent of a single shot from a double portafilter?
How many single espressos would you do in a typical day? If you are asked to produce a good many of them then you could think of picking up a second tamper just for those.
There have been many posts here about singles vs. doubles so I won't get back into it; however, where I work we simply don't pull them.
Honestly, the only time we're asked for "single" espressos is by Mediterranean clients, of which we have but few. Most people around here, myself included, are looking for a drink of about 60 ml. pulled from around 16 grams and that's what we are doing.
Getting back to your question: Many will say that a single basket makes a better single than a split double does. You should get some interesting answers here.
Your tamper is most likely 58mm and the single basket in question most likely has a ridge in it that is made for a 57mm tamper. You could spend $50 on a new 57mm tamper for your colection or you could spend $10 on a new single basket. This is the one I would buy http://www.espressoparts.com/F_869?&search_id=948407
I hope this helps
To the original question: "Is there a legitimate way to pour the equivalent of a single shot from a double portafilter?" I say no. That truncated cone shape is really important for pulling shots with smaller doses using a standard espresso machine. To try smaller doses in a double basket would give you a really shallow bed and a flawed extraction.
I think the suggestion to pick up a new single basket is a good one. At 6 bucks plus shipping, that's certainly the easiest idea.
The challenge will be in getting a good extraction, even using the basket that'll fit your tamp. It'll take some practice. To get an idea of what you're facing, try pulling some shots with the basket you have either without tamping or with a NSEW using the grinder's "nose" tamper. You may find that a different grind setting is required to get a decent single, which is kinda impractical and not a way to reduce coffee waste. There are some good discussions on here about pulling singles by the way, so look around.
Thank you all for the replies. Given the information I've gathered through this discussion, I think I can justifiably just not use the single. That's really what i wanted, haha. Thanks again!