I've been making jam for about 25 years, and my answer is heck yes. And don't increase the lemon juice to the level of the full recipe unless you want the tartness. Keep an eye on your cook time because you have less volume. Enjoy!

I am a jammer, and I also say 'why not?' Might be a good idea to retain the measurement for lemon juice, though, just to be sure it's acidic enough to be safe.

Yes, but why not check out some recipes for smaller amounts? There are lots out there.

I'm not a jammer, but I can't see why not.