In a saucepan, combine the water, milk, butter, and a pinch of salt. Mix well and heat over medium heat until it comes to a boil.

Remove the saucepan from the heat. Add the cornstarch and mix quickly and continuously, then add the eggs one at a time, mixing gradually until you get a dough.

Return the saucepan to the heat and stir quickly for a few minutes until the dough pulls away from the sides of the pan.

At this stage, fill a piping bag with the choux dough and pipe éclairs in your desired shape.

Preheat the oven to 350°F (180°C) and bake for 20 minutes without opening the oven door.

After 20 minutes, remove the éclairs from the oven. Prepare the tuna mousse by mixing the tuna in oil, processed cheese, and crème fraîche together.

Fill the inside of the éclairs with the tuna mousse and decorate with a little crème fraîche and half a teaspoon of saffron.