A large pot, like a Dutch oven, of melted shortening and a thermometer will work just as well as a deep fat fryer for donuts. That’s how my grandma always made her donuts. The temperature of the shortening is the key…not the container it’s heated in, as long as the pot is large enough.
Most donut recipes call for the oil to be heated to 375 degrees. And, don’t overcrowd the pot when you fry them.