6. To make the béchamel, add the remaining butter to a saucepan and leave it over low heat until it melts. Then add the butter and stir. Add the milk little by little and stir until the béchamel is made.
7. Grate the cheese and add it to the béchamel, and cook for another 3 minutes so that the ingredients are well integrated. Season with salt and pepper and stir again.
8. Subsequently, we add the leek to the mashed potatoes and season with salt and pepper. We mix well. We also peel the eggs and cut them in half.
9. Grease a baking dish with a little oil and add the leeks with the mashed potatoes. Smooth and place the eggs on top, pressing a little with your fingers.
10. Pour the béchamel on top and put the tray in the oven. We cook at 180º C for a quarter of an hour.
Finally, all that remains is to add a little chopped parsley, if you like it, and serve immediately. Delicious!