Prepare the Potatoes and Eggs: Peel the potatoes and cut them into evenly sized 2-3 cm cubes. Place them in a steamer. Add the eggs into the steamer as well (they can be placed on the steaming rack). Bring the water to a boil over high heat, then reduce to medium heat and steam for 15-20 minutes. The potatoes should be easily pierced with chopsticks, and the eggs should be fully cooked. Remove and allow to cool.

Prepare the Onion and Spring Onion: Peel and finely chop the onion. Place the chopped onion into a bowl and set aside. Wash and chop the spring onions into small pieces and set them aside for later use.

Prepare the Tuna: Open the can of tuna and drain the excess olive oil using a fine mesh strainer. Transfer the drained tuna into a bowl and add the chopped onion, spring onion, sea salt, black pepper, and lemon juice. Stir well to combine.

Mix the Salad: Once the eggs have cooled, peel and chop them into small pieces. Separate the egg yolks and mash them into a fine puree. Add the mashed yolks and chopped egg whites into a bowl. Once the steamed potatoes have cooled slightly, add them to the same bowl. Then, add the prepared tuna mixture and stir well. Finally, pour in 50 ml of warm milk and continue stirring until all ingredients are well mixed and the texture becomes sticky.