In a saucepan, combine water, butter, sugar, and salt. Bring to a boil over medium heat.
Reduce heat to low and add the flour. Stir continuously until the mixture forms a ball and pulls away from the sides.
Transfer dough to a bowl and let cool slightly. Beat in eggs one at a time, then mix in vanilla.
Spoon dough into a piping bag fitted with a large star tip.
Pipe donut rings onto parchment paper squares.
Heat oil in a deep fryer or large pot to 350°F (175°C). Fry donuts until golden brown, flipping once.
Combine sugar and cinnamon in a shallow bowl and toss warm donuts in the mixture.
For the filling, heat cream and pour over chopped chocolate. Let sit 2 minutes, then stir until smooth.
Pipe chocolate ganache into the center of each donut using a piping bag fitted with a small tip.
Serve warm and enjoy!