In a saucepan, bring the water, butter, and salt to a boil. Remove from heat and add all the flour at once. Stir with a wooden spoon until you get a dough (panade). Then, cook the dough over medium heat, stirring until it pulls away from the sides of the pan.

Let cool for 5 minutes, then add the eggs one at a time, mixing well after each addition.

Fill a piping bag and pipe the dough into éclair molds. If you don't have molds, shape the dough into logs. Brush the éclairs with the egg yolk and water mixture, then sprinkle with sesame seeds.

Bake for 10 minutes at 400°F (200°C), then 15 minutes at 350°F (180°C). Do not open the oven door during baking. When done, turn off the oven and leave the éclairs inside for 5 minutes. Then remove and let cool.

For the filling: cook the 2 salmon fillets in the microwave. Once cooked, mix them with the cream cheese, chives, lemon juice, salt, and pepper. Take the éclairs and cut them in half. Spread the filling inside. Close the éclairs and lay slices of smoked salmon on top. Serve cold.