In a medium saucepan, bring the water, butter, sugar, and salt to a boil over medium heat.

1. Once the butter has melted and the mixture is boiling, remove from heat and stir in the flour. Mix until a dough forms and pulls away from the sides of the pan.
2. Return the saucepan to the stove over low heat for 1-2 minutes, stirring constantly to dry out the dough slightly.
3. Remove the dough from the heat and let it cool for 5 minutes. Then, add the eggs one at a time, mixing well after each addition. Once all eggs are incorporated, stir in the vanilla extract.
4. Heat the vegetable oil in a deep frying pan or pot to 350°F (175°C). Carefully drop spoonfuls of the dough into the hot oil, frying the zeppole in batches for about 3-4 minutes per side, or until golden brown.
5. Using a slotted spoon, remove the zeppole from the oil and place them on a paper towel-lined plate to drain excess oil.
6. If filling the zeppole, use a piping bag to fill the center with pastry cream or your desired filling.
7. Dust the zeppole with powdered sugar just before serving.