In a heavy pot, bring water, butter, sugar, and salt to a rolling boil over medium-high heat.
Add flour all at once and stir vigorously with a wooden spoon until a smooth ball forms (1-2 minutes).
Cook dough for 3-4 minutes to dry slightly. Transfer to mixer and cool for 1 minute.
Add eggs one at a time, mixing thoroughly after each addition until shiny and elastic.
Transfer dough to pastry bag fitted with star tip. Pipe 3-inch rings onto greased parchment squares.
Heat oil to 370°F (188°C). Fry crullers 2-3 minutes per side until golden. Drain on wire rack.
Mix powdered sugar with water/milk to create glaze. Dip cooled crullers and let set.
Notes
For vegan option: Use plant-based butter and substitute eggs with aquafaba. Store unglazed crullers in airtight container for 2 days or freeze up to 1 month.