Bring the water, butter, sugar, vanilla, and salt to a boil in a small saucepan over medium heat. Remove from the heat and add the flour all at once; stir vigorously until the dough pulls away from the pan and forms a smooth mass. Let cool for 5 minutes. Add the eggs one at a time, beating briskly with a wooden spoon or silicone spatula until the dough is smooth, soft, and glossy.

Fit a piping bag with a large star tip and transfer the dough to the bag. Heat the oil in a medium pot to 320°F/160°C. Pipe short 1½–2 inch/4–5 cm strips directly over the pot, cutting each with kitchen scissors into the oil. Fry in batches, turning as needed, until puffed and deep golden, about 4–5 minutes. Transfer with a slotted spoon to a wire rack to drain briefly.

Combine the sugar and cinnamon in a bowl. While still warm, toss the churros bites in the cinnamon-sugar mixture. Serve immediately with milk chocolate ganache.