Pre-heat the smoker to 180-225ish. 225 is always my go-to, RecTeq has "XTREME SMOKE" at the 180 level - we're only going to about 110 internal temp, so it all depends on how long you want to spend.
Season that lamb with the rosemary, basil, thyme, and S&P.
Throw the meat on the grates and remove after IT 110.
As you crank your pellet smoker to 450+, lets get that reduction ready to go.
Brown your shallots, and add vinegar/chicken broth. Let it go over medium-high for 5 minutes (reduced). Throw the butter in there, stir it up and keep it on low while you finish off the meat.
Sear the meat, preferably on your GrillGrates, until your IT is 135ish. (or your preferred temperature).
Remove from grill, plate, and drizzle that balsamic goodness on there. (Don't forget to turn off the burner, I know I said 'low' earlier, but just to make sure)
Eat!