For the smashed sweet potatoes: Heat cream and butter in a medium saucepan until melted together. Add sweet potatoes and gently simmer, covered, stirring frequently, until potatoes are super tender, about 30 minutes. Add maple syrup and mash with a potato masher until smooth and uniform. Season to taste with plenty of salt and pepper. Cover and keep warm.
For the salmon: Heat olive oil in a 12-inch nonstick skillet over medium-low heat. Sprinkle salmon with salt and pepper all over. Lay in pan, skin-side down, and let cook, undisturbed, until skin is very crispy, 5 to 6 minutes. Gently flip the salmon and add butter, thyme and garlic and cook until salmon is desired temperature, 3 to 4 minutes for medium.
For radicchio: Zest orange, then cut away the pith with a knife and cut the segments free into a bowl, reserving any juice. Whisk together the orange juice, zest, Dijon, vinegar and shallot in a small bowl until combined. Slowly drizzle in olive oil, whisking, then season to taste with salt and pepper. Combine radicchio and watercress in a large bowl, then drizzle with vinaigrette, toss and season to taste.
Divide sweet potatoes among four plates, then top each with a crispy salmon fillet. Add a handful of salad on the side of each, then top salad with orange segments and drizzle the salmon with the butter sauce from the pan.