In a medium saucepan, add potatoes and 1/2 tsp salt, cover with water. Bring to boil, then reduce to simmer. Cook until fork tender and drain.
In another saucepan, add the butter, brown sugar, pinch salt, pineapple juice, cinnamon and nutmeg. Bring to a boil and simmer until thickened some - won't be real thick, more like a glaze. If you want a thicker glaze, add a small amount of corn starch to the pineapple juice before adding.
Once sauce is to desired thickness and potatoes are cooked. Add the drained pineapple to the glaze and cook until heated through. Stir in the vanilla.
Gently toss the sweet potatoes with the glaze, being careful not to break up potatoes too much. Heat through for a few minutes and pour into a serving dish. Sprinkle with pecans if using.