Preheat oven to 350 degrees.
Cut all of the skin from the potatoes, slice them into about 1/2 thick slices and rinse them thoroughly.
Place the yams In a baking dish and vanilla flavoring.
Then season the yams with cinnamon, nutmeg and sugar.
Using your fingers, massage the seasonings throughout all of the yams.
Cover with foil and bake for about 1 1/2 to 2 hours. (Until the yams are fork tender, but not falling apart.)
Remove from oven, add butter slices throughout the baking dish and recover to allow the butter to melt. (No more than 5-10 minutes)
Remove the yams from the oven and spoon the butter over the yams until all of the potatoes have been moistened.
Serve and enjoy.