Mix the flour with the baking powder and salt, sift together in a bowl. Add the 2 egg yolks, gradually adding the mineral water. Beat the dough with a mixing spoon until it is pliable and bubbles. Dice the rolls or toast bread and roast all over in the fat. Let cool down briefly and mix into the dough. Let it rest for a while.
Form 2 smaller rolls with floured hands, add to bubbly boiling water and let simmer for 20 minutes. Lift out with a wide slotted spoon and cut into slices with a twine.