Southern candied sweet potatoes

2 cups white sugar 
1 teaspoon ground cinnamon 
1 teaspoon ground nutmeg 
1 pinch salt 
1/2 cup butter 
6 sweet potatoes, peeled and sliced 
1 tablespoon vanilla extract
How to make it:
In a small bowl, mix the sugar, cinnamon, nutmeg, and salt together.
Melt butter in a large skillet over medium heat; add sweet potatoes, and stir to coat. 
Sprinkle sugar mixture over the sweet potatoes, and stir. 
Cover skillet, and reduce heat to low. 
Cook, stirring occasionally, for 1 hour, or until the sauce is dark and the potatoes are candied. 
They should be tender, but a little hard around the edges.
Stir in vanilla, and serve.