Add 2-inch oil to a large pot and heat to 375˚F (190˚C).
In a medium saucepan on medium-low heat, add water, butter, sugar and salt. Cook until butter melts completely.
Lower the heat and add flour. Use the wooden spoon to mix vigorously until well combined.
Transfer the dough into a large mixing bowl. Let it cool off slightly, about 3-5 minutes, then add eggs, one at a time. Mix the eggs with the dough using a hand-mixer or wooden spoon. (Make sure your dough is not too hot, otherwise the eggs will scramble when added to the dough.)
Check the temperature of the oil, if it’s ready, it’s time to fry the donuts. Use a small spoon to spoon out the batter, and then use another spoon or spatula to scrape the batter into the oil. Make sure to lower the spoon into the oil very gently so that you won’t splash the oil onto yourself.
Cook in batches and fry 10-12 donuts at a time. Fry for 4-5 minutes for each batch until they turn golden brown. You’ll need to turn them over from time to time to make sure all sides get cooked properly.
Remove cooked zeppole from the oil using a slotted spoon and place them on a paper towel lined plate.
Dust with powdered sugar and serve warm.