In a saucepan, combine the milk, water, butter, salt, and sugar. Heat over medium heat until the mixture starts boiling. Remove from the heat and add the flour all at once. Mix with a rubber spatula until no dry ingredients are left.

Bring back to the heat and cook the dough for 2 minutes, mixing continuously with the rubber spatula until a whiteish film forms on the bottom of the pan and the dough forms a ball with a homogeneous consistency. Remove from the heat.

Place the dough in a stand mixer fitted with a paddle attachment (you can also use a bowl and a rubber spatula or spoon). Beat the dough on low for a minute or until it’s not quite hot to the touch but still warm (the ideal temperature should be 110F-140F or 43C-60C ).

Gradually add the eggs, beating on medium speed until fully incorporated. Scrape the sides and the bottom of the bowl and beat one last time just for a few seconds to mix. The dough should be smooth and when you lift the paddle, it should slowly fall from it leaving a V-shaped tail. It should be firm enough to hold a shape when piped out but moist. If this texture is achieved before all eggs are incorporated, stop adding them. If the texture is not there yet after you’ve added all the eggs, you need to add ¼ - 1 extra egg.

Transfer the dough into a piping bag fitted with a round nozzle (such as Wilton 2A). Keep the piping nozzle facing straight down toward the piping surface (0.5” or 1 cm away from it) and pipe 30 even 1 ½" or 4cm rounds. Apply an even pressure, letting the rounds expand a little bit up and sideways. Leave 1" in between them. Work in batches if needed. The dough can wait in the piping bag while the first batch is in the oven. Dampen your finger with water and press down all the pointy tails on top of each round.

Bake one batch at a time at 375F (190C) for 25-30 min, or until puffed up, golden brown, and crispy. The baking time will vary on the size of your pastries. Baking eclairs can take up to 40 min.

Remove from the oven and let cool down on the baking sheet for 10 minutes, then place on a cooling rack to cool down completely. Pipe the second batch and bake.