Melt the butter, syrup, and brown sugar and let cool until lukewarm.
Blanch and chop the almonds, and add to a large mixing bowl together with the flour, cinnamon, allspice, ground cloves, ginger, and orange zest. If using potash, mix it with one tablespoon of water and add to the dry ingredients. Or if using baking soda instead, add it to the mixture.
Add the butter mixture to the dry ingredients, mixing first with a spoon and then kneading the dough together with your hands. Roll the dough into a long sausage, as thick as you would like the cookies to be. Wrap the sausage in plastic wrap, and if the dough is very soft, you can wrap it again in baking paper so that it keeps its round shape.
Leave the dough in the fridge for at least 4 hours, or overnight.
Preheat oven to 355°F (180°C) and line a baking sheet with baking paper.
Slice the cookie dough into thin slices and set on a baking sheet. The cookies won't spread too much in the oven, but leave a bit of space between each. Bake for about 10 minutes, until the bottoms turn golden.
Cool on a wire rack. The cookies will harden as they cool.