Heat the butter, sugar and syrup in a saucepan until the sugar melts. Turn off the heat.
Mix the flour in a mixing bowl with the spices.
Mix the baking soda with 1 tsp water.
Beat the eggs slightly.
Make a well in the middle of the flour mixture, then add the sugar syrup, eggs and baking soda. Mix gently with a wooden spatula, then rest in the fridge, covered, for about an hour.
Knead the dough on a lightly floured board. If the dough is still too soft, put it back to the refrigerator for a bit longer (see Tips).
Preheat the oven to 190°C.
Make two balls from the dough and roll each out to a 5mm thick pastry. Using Christmas motif cutters, stamp out shapes. Re-roll any leftover dough and press out more cookies.
If you want to hang the biscuits on the Christmas tree, then using a straw push out holes on the top of each biscuits (at least 1 cm in from the edge)
Place the cookies on non-stick or lined baking trays and bake until golden, for about 10-12 minutes.
Leave to cool on a wire rack.
Decorate them when completely cooled.