It happens every year at this time — I get in that springtime color mode and spin up a bunch of yummy fiber to compensate for the grey outside. This is superfine merino that I paint-dyed this weekend, spun into a controlled, regular thick-thin for one ply, and much thinner for the second ply. The yarn was then spiral plied together, much tighter than I normally would. Turns out to have been a successful experiment, as it's perfectly balanced.
The technique works great on merino and other short fibers in my experience. It involves, instead of smooth, steady drafting, a pinching and tugging motion with the drafting fingers, letting go over the thick areas, and drafting to spin the thin areas tightly.
I'm completely delighted, and that's not something that's been a common experience this winter.