In a large bowl, whisk together the flour, cornstarch, sugar, baking powder, and salt for the dough.
In a separate bowl, whisk the egg and milk. Add the wet ingredients to the dry ingredients and mix until just combined. Do not overmix.
If your potatoes are not already cooked, boil or steam them until tender. Dice them finely. You can also use leftover mashed potatoes if they are firm enough.
Insert a skewer into each sausage. Make sure they are firmly in place.
Dip each sausage into the prepared dough, ensuring it is fully coated. Let any excess drip off.
Immediately roll the dough-coated sausage in the diced potatoes, pressing gently to adhere. You can also add a layer of panko breadcrumbs for extra crispiness if desired.
Heat the vegetable oil in a deep pot or Dutch oven over medium-high heat to about 350°F (175°C).
Carefully place the coated corndogs into the hot oil, being careful not to overcrowd the pot. Fry for 3-5 minutes, turning occasionally, until golden brown and crispy.
Remove the corndogs from the oil and place them on a wire rack to drain excess oil.
Serve hot with your favorite dipping sauces like ketchup, mustard, or sriracha mayo.
Notes
For an extra touch, you can sprinkle sugar on top of the corndogs after frying, or add a sprinkle of cheese powder for a savory twist.