In a container on the stove top, put the water with the butter, sugar and salt until the butter melts.
Once the liquid comes to a boil, add the flour in batches and stir vigorously until you get a homogeneous mixture. Once it begins to separate from the walls of the dish, remove it from the heat. Place the dough in a bowl and add the eggs one at a time, while stirring constantly.
Use a pastry bag to spray thus prepared dough onto an oven dish with baking paper into small round or oblong shapes. Put them to bake for about half an hour in a preheated 365°F (185 °C) oven. After 30 minutes, reduce the heat and allow them to bake until ready. Leave the baked eclairs with the oven door open to cool.
For the cream, beat the eggs with 1 cup of milk and the flour. Put the remaining milk to boil with the sugar and while stirring, add the egg mixture. Once thickened, remove it from the heat and add the vanilla and butter. Fill the eclairs with the thus prepared cream.