Position rack in the center of the oven.

Preheat oven to 425 degrees Fahrenheit.

Cut a piece of parchment paper to fit a non-air-cushioned baking sheet.

Lightly butter the baking sheet and cover with parchment paper.

Fit a pastry bag with a 1-inch tip.

In a 2-quart saucepan, bring water, salt, and butter just to a boil until butter melts.

Remove from heat.

Add flour all at once and beat vigorously with a wooden spoon until blended.

Return pan to stove and continue to beat over low heat until the mixture is smooth, shiny, and pulls away from the sides of the pan, about 30 seconds.

Remove from heat.

Beat in eggs, one at a time, ensuring each is fully incorporated.

The finished dough will look shiny.

Fold the top third of the pastry bag down over your hand and scrape the dough into the bag with a spatula.

When two-thirds full, twirl the top of the bag until all the air is out.

Continue to twirl the bag and apply pressure with one hand, using your other hand to steady the tip.

Gently squeeze dough onto the baking sheet to form 13 mounds, each about 1 1/2 inches in size.

Bake for 20 minutes.

Remove from oven.

Slit puffs on either side about halfway through with the tip of a sharp knife.

Return puffs to oven for 15 minutes.

Remove to cooling rack.

When cool, split each puff in half from side to side.

The puffs should be light and browned.

If there is any wet dough inside, pull it out with your fingers.