For the best rise, measure flour accurately and ensure the dough cools slightly before adding eggs so they don’t scramble; the finished choux should be pipeable but not runny, so if it’s too stiff add a teaspoon of beaten egg, and if too loose refrigerate briefly. Bake until well browned to avoid collapse, and do not open the oven during the first 20 minutes. If shells feel soft after cooling, return them to a 300°F (150°C) oven for 10 minutes to dry. Eclairs can be filled with pastry cream instead of whipped cream, and unfilled shells freeze well in an airtight bag for up to 2 months; re-crisp at 325°F (165°C) for 5 to 8 minutes before filling.