Prepare the dough by boiling the water, adding the butter, then all the flour at once and stirring vigorously with a wooden spoon until homogeneous. Once the dough starts to separate from the pot, remove it from the heat.
Once cooled, add the eggs 1 at a time to it, while stirring with a wooden spoon. Onto a tray with baking paper, put 1 tablespoon of the dough at a time.
Put the éclairs to bake in a moderate oven, at 356°F (180 °C) for 30 minutes. Do not open the oven until the eclairs are ready. Then, open it and leave them to cool in the oven.
Meanwhile, prepare the cream by boiling the milk with the sugar. Beat the egg yolks with the flour with a little of the milk and add this mixture to the milk while stirring.
Once thickened, remove it from the heat, flavour it with vanilla and stir until cooled. Then mix it gently with the egg whites beaten into snow, and finally, with the cream beaten to snow. Put the cream into an icing piping syringe with a thin tip and fill the eclairs.
You can even cut them in 2, then fill each half with the French cream and stick them back together again.