Go to the Recipe: Perfect Éclairs
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Can I ask, why not use plain pastry creme for the filling? Will you not be able to pipe into the prepared shell?
You are welcome to use plain pastry cream for the filling, but it's nontraditional. I'd chalk that primarily up to:
Pastry cream is thicker and "gooier" than crème légère. The eating experience would read a little richer and eggier. Crème légère tends to read lighter, more whipped, less pudding-like, and it won't burst out as quickly as pastry cream when you bite into the éclair.
But to answer your question, yes, you can definitely pipe plain pastry cream into your éclairs, and it should pipe reasonably well. If you wanted a little extra stability/pipe-ability (and a hedge against weeping/syneresis), I would melt a sheet of bloomed gelatin into the pastry cream off heat after cooking, before cooling and whipping.
Hope this helps!