Wake up your starter and allow to form light bubbles on top. Normally it needs 20-30 minutes depending where you store it.
In a large bowl mix the flour with the fennel seeds and salt. Follow in with the levain and the water. Knead for 5-6 minutes and let it rest under a clean towel. You can return to it after 2-3 hours.
In the second round, you can fold in the walnuts. Lightly dust a clean worktop with flour and transfer the dough. This time you will knead lightly knocking off the air bubbles and folding in the walnuts a spoonful at a time. Cover and rest for 6-8 hours.
Before you bake, transfer the bread on the worktop. Tear apart a small portion of the dough. Then again cut in two to form 2 strings and place them across the top of you loaf.
To decorate, lightly brush with water and sprinkle the sesame seeds on top. Place your shelled walnut in the middle and cut with a sharp knife the side of the cross to help the loaf rise.
Bake for 15 minutes at 220C and lower the oven at 200 for 30-35 minutes. Remove from the oven and allow it to cool down on a clean towel or a rack.