Prepare the dough:
Sift the flour into a large baking bowl, sprinkle the salt on top and mix. Press an indentation in the center, pour in the sugar and sprinkle/crumble the yeast over it. Mix with a little flour and stir with half of lukewarm milk to form a paste.
While stirring in the bulge, stir in as much flour as you can until you get a porridge-like consistency. This will leave about half of the flour !
Put the baking bowl in a plastic bag, cover with a kitchen towel and let rise in a warm place [25 to 42 degrees , above 42 degrees the yeast is killed] for 15 min [the porridge has doubled in size and shows large bubbles].
Sprinkle a little flour over the yeast piece and add the rest of the warm milk and the melted lukewarm cooled fat.
Mix everything well and knead in about 15 min to a smooth dough that no longer sticks and begins to show bubbles.
[Keep to the kneading time! The dough will be quite smooth, you will have the impression it is hollow inside when you drop it on the table].
Shape the dough into a ball and place it on the bottom of the baking bowl sprinkled with flour. Put it back in the plastic bag and let it rise, covered with a kitchen towel, in a warm place for 30 min. until it has doubled in size.
Cut the peeled bananas into narrow slices, sprinkle with juice of one lemon and marinate for 10 min with the lid closed.
Roll out the dough into a rectangle of 30*40cm, fold the