Place oven rack in the middle position. Preheat the oven to 450°F. Slice each yam, skin–on, lengthwise into 3/4-inch thick slices. Now cut each yam slice into 3/4-inch wide strips and place them in a bowl. Add the vegetable oil, salt, pepper and paprika and toss to coat. Arrange the yams in a single layer on a large, good-quailty, non-stick baking sheet. (The baking sheet needs to be around 11-inches wide, and 18-inches long. If too small the yam fries will be too crowded and won’t crisp up properly.) Bake the yams in the oven for 25 minutes. Turn the oven to broil and cook until the yams are crispy on top, about 3 to 5 minutes.
Note: Instead of salt, pepper and paprika, flavour the yam fries, to taste, with your favourite seasoning salt, Cajun spice, or with curry powder.