Parboil the potatoes for approximately 5 to 6 minutes in salted water. Drain and allow to cool to room temperature.
Meanwhile, saute the diced onions in the oil plus 1 tablespoon of the butter until richly browned and caramel colored. This step insures that all of the onion's sweetness is developed. Cool the onions, then mix with the cooled potatoes, maple syrup, and cinnamon.
Melt the remaining buttter in a 10-inch non-stick saute pan over medium heat and add the potato/onion mixture. Take care to pack the mixture tightly in one neat layer to saute and brown.
Using the back of a spoon, form the potato and onion mixture into a rounded cake. When the potatoes and onions begin to adhere and brown, they can be flipped over using a large spatula or the back of a plate. Alternately, they may be simply stirred to crisp evenly. If you've flipped them, brown the second side. Serve hot.