Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit), conventional oven.
Melt water and butter in a pot. Add the flour and stir well and quickly until a thick and cohesive dough is formed.
Remove the pot from the heat. Wait 2–3 minutes, then add the eggs one at a time while vigorously stirring, until a smooth and elastic dough is obtained.
The dough should be soft but firm enough not to slide out when piped onto a baking sheet.
Put the dough into a freezer bag, cut a hole in the corner, and pipe buns onto a baking sheet with parchment paper. The buns should be about the size of an egg.
Bake for 30 minutes until the buns are golden. If they look done after 20 minutes, turn the oven down to 165 degrees Celsius (329 degrees Fahrenheit) for the last 10 minutes. Cool on a wire rack.