Preheat oven to 350°F. Oil the sweet potatoes and roast on rimmed baking sheet until very tender, 1 to 1 ½ hours. (You can nook them in the microwave to speed the roasting time!)
Cool slightly. Cut each potato in half and place the flesh of the top halves in a bowl—it should just fall out of the skin. Gently scoop the flesh out of the bottom halves and add it to the bowl, leaving a little around the edges for stability. Mix in the crème fraiche, 4 Tbs. butter, syrup, bourbon, 1 tsp. cinnamon, 3/4 tsp. nutmeg, 1 tsp. salt and pepper to taste. Using a hand mixer (or immersion blender), puree until smooth.
Scoop the potato puree back into the bottom halves. Mix the remaining 2 Tb. of butter and ¼ tsp. nutmeg with the panko and chopped nuts. Salt and pepper to taste. Sprinkle the mixture over the tops of the sweet potatoes. Bake another 15-20 minutes until warmed through and golden on top!
These can be made 2-3 days in advance. If coming out of the fridge, bake 30-40 minutes--until warmed through or cheat and rewarm in the microwave. *smile* I won't tell!