Why is strong flour used when making choux pastry?

You are making a type of pastry used for choclate eclairs, profiteroles, croquembouche or Paris Brest. It must bake quickly in the oven, puffing up so that it is filled with air, but with the pastry setting crisp and firm so that it retains its shape when you take it from the oven.

A strong flour has more gluten (the protein in wheat). Protein hardens when it is heated. If the choux is to be filled with custard or cream, for example, it is important that it is strong and dry so it doesn't turn wet and flabby.

When you take choux buns from the oven pierce them immediately with a sharp knife or cut a small cross in the bottom before placing them on a rack to cool. This allows the steam to escape and also creates a hole through which to place the nozzle of the piping bag when you fill them. They can be quite brittle so you want to reduce the handling as far as possible. Don't fill them until the last possible moment before they are served.