Wash & slice sweet potatoes in 1/4 inch wide sticks.  Soak sliced potatoes in a bowl of cold water for an hour.  Pour out the water, rinse & pat dry.  Line 2 baking sheets with foil, parchment, or something that won't stick to the potatoes. Spray with non-stick spray.

Melt a stick of butter in large bowl or pan.  Add salt, chili powder and pepper to melted butter & set aside.

Place 1/2 of your (patted dry) potato sticks into a giant zipper top bag and sprinkle in 1 tbsp starch.  Shake it all up and dump your starched potato sticks into the bowl of seasoned butter.  Toss them around in the butter mixture to coat & arrange them in a single layer on one of the baking sheets.

Next bag & starch the other half of the potato sticks, then toss them in the butter mixture & arrange on the second baking sheet.

Bake in 425 degree oven for 15 minutes.  Put some space between the 2 sheets - you want everyone to have room to crisp up.

After 15 minutes, flip all the taters over & bake another 10 minutes (total baking time: 25 minutes).

Once they are done, remove from the oven and let cool slightly.  Add more salt to taste.  Serve warm, not hot.  This will make them crispier.

I think the best sauce for sweet potato fries is a simple Russian Dressing.  Your favorite mayo with a little ketchup stirred in.  Yum!