Scrub potatoes and cut a small, deep slit in the top of each. Set on a sheet pan on the center rack of a preheated 375 degree oven and bake for about an hour, or until potatoes are tender when pierced with a fork.

Meanwhile, peel and trip the carrots and cut them into 1” lengths. Put them in a saucepan and add the water, sugar, 1 ounce of the butter, then salt and pepper to taste. Set over medium heat, bring to boil, and cook uncovered until the water has evaporated and carrots begin to sizzle in the butter, or about 30 minutes. The carrots should be tender. If not, add a little water and cook until the carrots are done and all the liquid has evaporated.

Scrape out the flesh of the sweet potatoes and combine with the carrots in the bowl of a food processor fitted with a steel blade. Add remaining butter and crème fraiche and process until very smooth.

Add nutmeg, and season to taste with salt and pepper. Add cayenne, if desired and process briefly to blend.

To reheat, transfer to an ovenproof serving dish and cover with foil. Heat in a preheated 350 degree oven for about 25 minutes or until steaming hot.