Tuna and Swiss Chard Tart

Place the butter at room temperature in a bowl and work it with a wooden spoon until creamy.

Add salt, pepper, sugar, egg yolk, and water at room temperature. Mix well until the mixture is smooth.

Finally, add the flour, previously sifted, and combine until you form a smooth dough ball. Cover with plastic wrap and refrigerate for 2 hours.

In a large skillet, heat the oil and butter. Sauté the finely chopped onion and bell pepper.

Add the well-drained and chopped Swiss chard to the skillet, followed by the crumbled tuna. Cook for 2 minutes and remove from heat.

Once the mixture has cooled slightly, add the coarsely chopped hard-boiled eggs and the sliced olives.

Roll out the pastry and line a tart pan with it. Add the cooled filling on top of the pastry.

In a bowl, mix the eggs with the béchamel sauce and season with salt, pepper, and nutmeg.

Pour this mixture over the filling and sprinkle with grated Parmesan cheese.

Bake in a preheated moderate oven at 180°C (350°F) for about 30 to 35 minutes, or until the surface is golden brown.