Crush all spices in a mortar and pour into a container. Pour 700 ml of vodka (40% by volume), shake heartily and close the jar. Put in a light place, infuse the mixture for about 14 days, shaking well once every 2 days.
Add 250 ml of sugar syrup to the mixture, mix everything together, then filter. Transfer to a bottle rinsed with boiling hot water and close tightly.
Shelf life: Well closed and placed in the dark, this bitters, a little bit sweeter, can be kept almost indefinitely.