The sweet potatoes should be steamed about 15 minutes, or until fork tender, but should not be soft or mushy. The sweet potatoes can also be microwaved in a glass pie pan with 2 tablespoons water, pan covered with plastic wrap, for about 7 minutes.
Meanwhile, in the bowl of a food processor fitted with the metal blade, add the flour, sugar, baking powder, cinnamon, nutmeg, salt, and pepper and pulse until mixed. Add the sweet potatoes, eggs, orange juice, orange zest, and melted butter and process until smooth. Line a baking sheet with 2 layers of paper towels.
Put a 10-inch flat metal pan or skillet over medium-high heat, add the vegetable oil, and swirl to coat the bottom of the pan. The pan is ready when the oil bubbles.
Add a heaping tablespoon of batter to the hot griddle and spread it out with the bottom of the spoon until it is 3-inches in diameter. Add more latke batter but do not overcrowd the pan. Cook until the latkes begin to bubble around the edges, about 1 1/2 minutes. Gently turn the latkes over and continue cooking until the bottom turns golden brown, about 1 to 1 1/2 minutes. Do not overcook the latkes.
Place the fried latkes on the prepared baking sheet and cover with 2 additional sheets of paper towel. Press gently to remove the excess oil. Serve the latkes immediately or put them onto a baking sheet and keep them warm in a 200 degree F oven. Latkes are best served the day they are made. Serve with sour cream, applesauce or confectioners' sugar.
Leftover latkes can be wrapped in plastic wrap, stored in the refrigerator, and reheated in a 300 degree F oven the next day.
Alternatively, you can drop a tiny bit of batter into the pan: when the batter begins to brown, the pan is ready.