Pick potatoes that are all about the size of a Ping-Pong ball so that they finish cooking at the same time.
Preheat oven to 375º. Rub the potatoes with the oil and place on a baking sheet. Roast for 25 to 30 minutes, or until just tender. Cool to room temperature.
In a small bowl, whisk together the ricotta and the egg white until smooth. Stir in the remaining ingredients and mix well.
Slice each potato in half. With a serrated citrus spoon or a slightly pointed teaspoon, scoop out a little of the flesh in each potato half. If the potato halves don't sit level, slice a tiny sliver off the bottom so they stand upright.
Preheat oven to 400º. Use a teaspoon to mound the ham-and-cheese mixture into the scooped-out potato halves. Place the filled potatoes on an ungreased baking sheet and bake for 12 to 18 minutes, or until hot and just beginning to brown on top.
How Kids Can Help: Measure and mix ingredients; scoop out potatoes and fill them.