Prick the sweet potato several times with a fork and place on a double layer of paper towels in a microwave. Cook at full power for 5 minutes; turn the potato over and continue to cook at full power until tender but not mushy, about 5 minutes. Cool 10 minutes. Halve the potato crosswise and scoop out the flesh into a medium bowl; discard the skin.
In a large bowl, combine the flour, salt, sugar, baking soda, and baking powder. In the bowl with the sweet potato, add the buttermilk, egg yolk, melted butter, honey, cinnamon, and nutmeg; whisk to combine. In a small bowl, beat egg whites until light and fluffy. Add sweet potato mixture and egg whites to the dry ingredients mixing until just combined. Let the batter stand for 1 hour.
Preheat oven to 350 degrees F. Toast pecans on a baking sheet in the preheated oven 10 minutes.
To make honey-cinnamon butter, combine butter, honey, and cinnamon and whip until light and fluffy. Set aside.
Heat a skillet over medium heat. Add batter by 1/2 cup pours and cook the pancakes, in batches, until golden brown on each side. Serve immediately with honey-cinnamon butter and roasted pecans.