Store the shells in an airtight container at room temperature for up to 1 day, or make them ahead and freeze for up to 1 month.
- 1/2 cup milk
- 1/2 cup water
- 6 Tbs. (3/4 stick) unsalted butter, cut into
- 1/4 tsp. salt
- 1 cup unbleached all-purpose flour
- 4 eggs
Meanwhile, in a small bowl, whisk 1 of the eggs. When the batter has cooled, add the egg and beat with the spoon until incorporated. Whisk each of the remaining eggs one at a time, then stir into the batter. After each egg is added, the mixture will separate and appear shiny but will return to a smooth paste with vigorous beating. Let the paste cool for about 10 minutes before shaping.
Position 2 racks evenly in the oven and preheat to 425°F. Line 2 half-sheet pans with parchment paper or aluminum foil.
To shape small puffs (ideal for profiteroles), fit a pastry bag with a 3/16-inch plain tip and fill the bag with the paste. For each puff, pipe about 1 tsp. of the paste onto a prepared pan, forming a mound about 1/2 inch in diameter. Space the mounds at least 2 inches apart to allow for expansion.
To shape large puffs (ideal for cream puffs), fit a pastry bag with a 5/8-inch plain tip and fill the bag with the paste. For each puff, pipe about 1 Tbs. of the paste onto a prepared pan, forming a mound about 2 inches in diameter. Space the mounds at least 2 inches apart to allow for expansion.
To shape logs (ideal for éclairs), fit a pastry bag with a 3/4-inch plain tip and fill the bag with the paste. Pipe out logs 4 inches long and 1 inch wide. Space the logs at least 2 inches apart to allow for expansion.
Bake the puffs for 15 minutes, then reduce the heat to 375°F and continue baking until golden brown, 5 to 10 minutes more for the small puffs and 15 to 20 minutes more for the large puffs and logs.
Remove from the oven and immediately prick the side of each puff or log with the tip of a sharp knife. Return to the oven, leave the oven door open and allow the pastries to dry out for 10 to 15 minutes. Transfer the pans to wire racks and let the pastries cool completely on the pans before filling.