Make the sauce. In a saucepan with straight sides on medium heat, add the balsamic vinegar, honey, rosemary, liquid smoke, a pinch of salt and a hefty grind of black pepper. Stir and cook on medium-low until it reduces and thickens into a sauce, about 20 minutes.
Saute the veggies. In your largest pan on medium-high heat, add the oil and the Brussels, minus the reserved stray leaves. Cook the Brussels until they are a deep golden to dark caramelized color on most of the surface, 15 to 20 minutes. Season with salt and add the onions to the pan. Toss to cook, wilt and caramelize, keeping the pan hot, until the onions are lightly browned, 10 to 15 minutes. Add the reserved leaves and cook, tossing, until they become golden as well.
Finish and serve. Add the pepitas and dried cherries to the pan and toss everything to combine and warm. Add the sauce and toss again. Season the pan with salt and serve.