Peel and wash the potatoes, cut them into large pieces, cover and cook in boiling salted water for about 20 minutes.
In the meantime drain the tuna and tear it to pieces. Grate cheese finely. Clean and wash spring onions and cut into fine rings.
Drain the potatoes and let them steam briefly. Press through a potato ricer or mash them finely. Quickly mix in butter, 75 g flour, cheese and 2 egg yolks. Stir in tuna and spring onions, season with salt and pepper. Pour the mixture into a bowl, cover with foil and leave to cool for approx. 30 minutes.
Whisk 2 eggs and milk. With floured hands, form longish sticks from 1 heaped tablespoon of potato mass each. Turn the sticks one after the other only in 50 g flour, shake off excess flour. Then whisk them in a whisked egg and finally in Panko. Refrigerate again for about 30 minutes.
Heat the oil in a wide pot (it is at the right temperature when small bubbles rise from a wooden stick held inside). Fry the sticks in portions, turning them occasionally until golden brown. Remove with a skimmer and let them drip off on kitchen paper. Serve with lemon wedges to drizzle on. Aioli is delicious with it.