Tuna and potato pie

Directions

1. For the béchamel sauce:
   Place the butter in a saucepan and heat over low heat. When the butter start to melt, add the flour with a little milk and whisk until the flour is dissolved. Gradually add the rest of the milk, increase to medium heat and stir until a homogeneous and creamy mixture, about 10 minutes.
2. Turn off the heat and season with a little salt, pepper and nutmeg. Mix the seasonings in the sauce and let cool. Béchamel sauce recipe.
3. Drain and shred the tuna with a fork; set aside.
4. Place the olive oil, the chopped onion and the peeled tomatoes cut into small pieces in a saucepan and cook over low heat until the tomato start to break down, stirring occasionally. Add the tuna and season with pepper and chopped rosemary. Stir and cook about 4 to 5 minutes, stirring occasionally.
5. Meanwhile, peel, wash the potatoes and cut into small cubes. Season with salt and fry in very hot oil. When the potatoes are fried, place them in a dish with absorbent paper.
6. Add the potatoes to the tuna pan, combine and turn off the heat. Let stand for 5 minutes.
7. Combine together the béchamel sauce, the egg yolk and a few drops of lemon juice.
8. Preheat the oven to 180ºC (350ºF).
9. Grease a pie pan (24 centimeters (9 1/2 inches)) with butter, line with the pastry and prick the bottom with a fork. Pour the tuna and potato mixture over the pastry, drizzle with the béchamel mixture and sprinkle with grated cheese. Bake until golden brown, about 35 minutes.
10. Turn off the oven and serve with lettuce and tomato salad.