Put the dates in a big bowl and cover with hot water. Leave at least 10 minutes.
Melt the butter and chocolate in a bain-marie.
Mix 2/3 of the dates in a food processor with a little hot water. Add water if necessary to obtain a pasty texture. Reserve the remaining 1/3 of dates.
In a big bowl, whisk the date purée and the butter-chocolate mixture.
Separate the egg whites and yolks.
Whip up the egg whites with a pinch of salt until stiff and foamy.
In the bowl, add the egg yolks and sugar and whisk the mixture. Then add the flour, the yeast and another small pinch of salt. Mix well.
Then, gently fold the egg whites into the dough.
Finally, cut the remaining dates in 2 or 3 lengthwise and add them to the preparation.
Optional: you can add coarsely crushed walnut kernels.
Pour the preparation into a rectangular cake tin.
Bake for about 35 minutes at 180°C (+/- 5 minutes). Check the cooking after 30 minutes with the tip of a knife.
