Preheat oven to 375°F (190°C).
To make the pastry shells: In a medium saucepan, combine 1 cup of water, butter, sugar and salt and bring it to a boil over high heat. When butter is melted and the mixture is boiling, add flour all at once, reduce the heat to medium and continuously stir until the dough will start to form into a ball. Keep mixing for another 3-4 minutes until light crust forms on the bottom of the pan.
Transfer the dough into a mixing bowl with paddle attachment and mix it for a few minutes on low speed until the mixture is cooled to room temperature.
Add the eggs one at a time, beating well after each addition. This will help to get egg absorbed into the dough quicker. Don’t add more than 2 eggs at a time. This is important, as you might not need to add all the eggs. The dough should be smooth and thin enough to fall into a ribbon, but too runny.
Transfer the batter into a pastry bag and pipe into 4-inch strips 3 inches apart. Level peaked tops with wet fingertip, if needed.
Bake for 30-35 minutes, or until the shells are puffed up and golden brown, rotating the sheets top to bottom and back to front once after first 20 minutes. When you take the éclairs out, it should stay puffed. If it falls flat, put it back in the oven, bake for additional 3-5 minutes, turn the oven off and let it cool in the warm oven.
Once cooled, cut the eclairs in half horizontally.
To make the pudding, in a heavy bottomed saucepan, place milk and slowly bring it to a simmer over medium heat. This’s called scalding the milk. Once you see small bubbles appearing on the surface, remove it from heat. Be careful not to boil it though, or it’ll scramble the eggs in step 3.
In a medium bowl, combine egg yolks, sugar, cornstarch, vanilla extract, vanilla bean paste and salt. Whisk the mixture until creamy and doubled in size.
To temper the egg mixture, slowly add 1 cup of scalded milk into the egg yolk mixture, while constantly whisking the mixture.
Transfer the tempered egg mixture into the remaining scalded milk. Cook the mixture over medium heat, stirring constantly for 8-10 minutes, or until the mixture is nice and thick.
Run the custard through a sieve for extra smooth texture.
Cover it with a plastic wrap so that it touches the surface of the pudding. This’ll prevent a layer of film from forming on top. Chill the pudding completely.
Whip heavy cream until hard peaks form. And gently fold into the chilled vanilla pudding until smooth.
Transfer the filling into a pastry bag with star tip (I used Wilton 1M).
Cut bananas into thin slices.
Layer banana slices on the bottom half of the éclair shells.
Pipe the filling and replace the top of the shells.
To make the chocolate ganache, in a small saucepan, bring heavy cream to a simmer. Do not boil.
Pour hot cream over chocolate chips, and let it sit for good 2 minutes. Then mix well until smooth for couple minutes.
Stir in butter to add some shine.
Pour chocolate ganache over the eclairs and serve.
Store the assembled eclairs in the fridge for up to 2 days.