Preheat the oven to 175°C (350°F).

In a large mixing bowl, cream together the butter and sugar until light and fluffy.

Mix in the dark syrup (or molasses).

In another bowl, whisk together the all-purpose flour, baking soda, vanilla sugar (or vanilla extract), and salt (if using).

Gradually add the dry ingredients to the wet ingredients, mixing until a cohesive dough forms.

Divide the dough into equal parts and roll each into a log approximately 5cm in diameter. Place on a baking sheet lined with parchment paper, allowing some space for the cookies to spread.

Bake in the preheated oven for about 10-12 minutes or until the edges are lightly browned.

Remove from the oven and let them cool on the baking sheet for a couple of minutes before transferring to a wire rack to cool completely.

Once cooled, slice the logs into 1cm thick pieces and serve.