Put the flours in a bowl and press a depression in the middle. Mix yeast, sugar and 100 ml of lukewarm water, pour into the hollow. Covered with some flour and let it rise for 10 minutes.
Add salt and another 200 ml lukewarm water. Work into a smooth dough with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for about 20 minutes. Knead the dough on a floured work surface and roll out into a 20 x 40 cm rectangle.
Separate the egg. Spread the dough with some beaten egg white and sprinkle with caraway and coarse salt. Roll up the dough from the long side and cut into 4 cm wide pieces. Using a floured spoon handle, press the pieces down firmly between the cut edges in the middle so that the sides curve up sharply.
Place the dough particles on a baking tray lined with baking paper. Whisk the egg yolks with a little water. Spread the French roll with it. Cover and leave to rise for 20 minutes. Bake in the preheated oven (electric cooker 200 ° C/ gas: level 3) for about 25 minutes.
Let it cool down on a cake rack. Serve with butter or finely sliced cheese. Makes about 10 pieces.