Peel the Roscoff onion, dice it and toss it in the butter. Add the potatoes cut into cubes and stew a little. But potatoes and onions shouldn`t turn brown. Then deglaze the whole thing with the milk, season and simmer gently for about 20-25 minutes.
Roast the diced toast in the remaining butter with the garlic and pour over the soup on the plate, sprinkle with freshly grated Parmesan.
The story of the Roscoff onion:
The Roscoff onion is a very old variety of onion and is slightly pink. Due to its good shelf life and its high vitamin content, it was a particularly sought-after food for seafarers who appreciated these properties on long sea voyages.
The English quickly found a taste for the delicious pink Rosscoff onion and the tradition of Johnnis, as the Breton onion sellers were called by the English, continues to this day.