Sweet Potato Rosti - "addictive as french fries"

I think of Rosti as a winter dish, but prepared properly, it can be as addictive as good french fries. In this recipe, I use a mix of sweet and regular potatoes. This keeps the Rosti from getting too sweet and the white potatoes add body.

Serves 6
2 Sweet Potatoes
2 Yukon Gold Potatoes
1 Medium onion
Olive Oil
1 Tbsp Butter
Salt and Pepper to taste
1 Nonstick pan that can be placed into a hot oven (Watch out for plastic handles) or grease a cast iron skillet.

1) Par boil all the potatoes (leave the skins on) about 20 minutes.
2) Cut the onion into quarters and thinly slice.
3) Saute the onions over medium heat. About 5 minutes.
4) Remove potatoes from heat. Empty water and let cool. Run under cold water to speed the process.
5) When cool enough to handle, remove skins from the potatoes.
6) Preheat oven to 350F
6) Alternating sweet and white potatoes, grate into large bowl.
7) Try not to mash the potatoes as you mix in the onions and mix the potatoes together.
8) Place mixture in nonstick pan or greased iron skillet.
9) Cook over medium high heat for 10 minutes.
10) Place dabs of butter on top or spinkle with olive oil.
11) Place in Oven, and bake for 60 minutes. If the top is not browning, turn on broiler before serving. If browning too much, lower heat or cover with tin foil.