Preheat oven at 180°C.

Prepare a baking tray of 40 x 20 cm or similar (mine was 35 x 27) with parchment paper or a silicon pad.

Melt the chocolate and the butter together. You can use a water bath, or use the microwave with sets of 10-20 seconds and mixing in between the sets. Chocolate should be completely melted.

With the help of a hand mixer, or a sand mixer with the whisk attachment, mix the eggs with the salt and sugar until they get fluffy.

Add the orange zest if you want. (optional)

Incorporate the chocolate mixture and fold with a spatula in upward downward movements, until the chocolate is incorporated.

Sift the flower on top of the chocolate and fold it lightly until all the flour is incorporated.

You can add now the optional ingredients, like nuts, raisins, etc.

Pour into the prepared baking tray and smooth the surface to get equal thickness overall.

Bake for 25 min at 180 °C.

Let cool in the tray for 5 min, then remove and cool on a cooling rack.