Place the sweet potatoes in a large pot and cover the potatoes with water
Bring to a boil for about 20-25 minutes, you want the sweet potatoes to be partially cooked
Drain them from the water and allow them to cool
While the potatoes cool make your simple syrup
Combine the sugar and water ,bring up to a boil and then slightly reduce the heat
Stirring from time to time you want it to thicken and reduce , this will take 25-30 minutes
When the syrup is thickened turn off the heat and stir in the vanilla
Preheat oven to 400 degrees
Now by hand peel the skin off of the sweet potatoes
Slice the sweet potatoes in long strips by slicing them in half length wise and then slice those halves in strips
Place the strips in a casserole dish..I used a 4 quart dish but a 9x13 baking dish would work also
Pour the simple syrup over the sweet potatoes
Slice the cold butter into small squares and evenly place them over the sweet potatoes
Mix the sugar and cinnamon together
Poor the cinnamon and sugar mixture over the top of the sweet potatoes
Bake uncovered for 25 minutes
Turn off the oven and do not open the door
Allow the sweet potatoes to set in the oven for one hour, if they sit for a little longer it's okay . The longer they sit the better they get