Combine milk, butter, sugar, and salt in heavy saucepan.
Cook over medium heat until butter is melted and sugar dissolved; stir constantly.
Add all the flour.
Stir vigorously with wooden spoon until mixture is smooth and leaves sides of pan, forming a ball.
Turn off heat; add 1 egg.
Beat until well mixed.
Continue adding eggs one at a time; beat well after each addition. (An electric mixer can be used to beat in eggs.)
Beat until smooth; cover lightly.
Let stand until cool.
Spoon pastry into icing bag with 1-inch plain piping tube attached; pipe out as desired onto lightly greased baking sheet.
Bake in preheated 450Â°F oven 8 minutes.
Reduce oven temperature to 350 Â°F; bake 20 to 40 minutes, depending on size of puffs or eclairs, until dry.
Cool on wire racks; fill as desired.