Preheat oven to 350°F. Grease a 9- x 13-inch baking pan, and set aside.

In a food processor fitted with the knife blade, process potato, carrot, and onion until they are ground very finely, stopping the machine and scraping down the sides with a rubber spatula as necessary. Pour the processed vegetables into a large bowl, and add oil and salt. Add potato starch or tapioca starch, 1 cup at a time. Keep adding more starch and kneed as you go along, until you have a dough-like mixture that holds together.

Press the kishka into the greased pan, and even out the top with the back of a rubber spatula.

Bake uncovered for 45 minutes. Set aside until just cool enough to handle.