In a medium saucepan, combine water, butter, and salt. Bring to a rolling boil over medium-high heat, stirring until butter is melted.

Remove the saucepan from heat. Add the all-purpose flour all at once. Stir vigorously with a wooden spoon until the mixture forms a ball and pulls away from the sides of the pan.

Return the saucepan to low heat and continue to cook, stirring for another 1-2 minutes to dry out the dough slightly. Transfer the dough to a large mixing bowl.

Let the dough cool for 5 minutes. Add the eggs one at a time, beating well with a wooden spoon or electric mixer after each addition, until fully incorporated and the dough is smooth and glossy. Stir in the vanilla extract.

In a shallow dish, whisk together the granulated sugar and ground cinnamon. Set aside.

Deep Frying: Pour vegetable oil into a deep pot or Dutch oven until it's about 2-3 inches deep. Heat the oil over medium-high heat to 350°F (175°C). Use a candy thermometer to monitor the temperature.

Carefully drop spoonfuls (about 1-inch size) of dough into the hot oil. Do not overcrowd the pot; fry in batches. (Alternatively, if using a piping bag with a star tip, pipe 1-inch lengths of dough and snip with scissors into the hot oil).

Fry for 3-5 minutes per batch, turning occasionally, until the donut bites are golden brown and cooked through.

Remove the donut bites with a slotted spoon and transfer them to a plate lined with paper towels to drain excess oil.

Air Frying: Preheat air fryer to 375°F (190°C). Lightly grease the air fryer basket with non-stick cooking spray.

Carefully drop spoonfuls (about 1-inch size) of dough into the air fryer basket, leaving space between them. Do not overcrowd.

Air fry for 8-10 minutes per batch, shaking the basket halfway through, until golden brown and cooked through. Repeat with remaining dough.

While still warm, immediately toss the fried/air-fried donut bites in the cinnamon sugar mixture until evenly coated.

Serve warm and enjoy your Sweet Churro Donut Bites!