6 sweet potatoes (about 12 oz. each)
4 tbsp. unsalted butter, softened
1/2 c. (packed) brown sugar
1/2 c. milk
1/2 tsp. cinnamon
1 tbsp. plus 1/4 tsp. salt
1/2 c. granulated sugar
1 egg
1/2 tsp. nutmeg (freshly grated)

Preheat the oven to 350 degrees. Place the sweet potatoes in a large saucepan and add enough water to cover. Add 1 tablespoon of the salt. Bring to a boil over high heat and cook until potatoes are soft, 30-50 minutes; drain well.

When potatoes are cool enough to handle, peel and place in a large bowl. Using a potato masher or a fork, mash the potatoes until smooth.

In a medium bowl, mix the butter and the sugars. Whisk in the egg until blended, then add the milk and mix well. Add to the potatoes and mix thoroughly. Season with the nutmeg, cinnamon and the remaining 3/4 teaspoon salt.

Transfer the mixture to large baking dish and smooth the top. Bake for about 1 hour, or until lightly golden. (The sham can be made up to 1 day ahead and refrigerated covered. Increase baking time by 5 minutes or so. It can also be baked and refrigerated up to 1 day ahead. Return to room temperature and reheat in a 350 degree oven.