Mix all the dry ingredients in a bowl. The flour does not have to be sifted. Then add water (slightly cooled).
After you stir very well, add the oil and rum essence. Add the crushed hazelnuts and leave a little to sprinkle on top.
Pour the mixture in a tray with baking paper, and sprinkle it with remaining nuts. Bake in a preheated 347°F (175 °C) oven for about 25-30 minutes.