Soak the Brussels sprouts in a large bowl filled with lightly salted water for about 15 minutes.
Meanwhile, sterilise three 450ml jars and their lids in boiling water for at least 5 minutes.
Drain the sprouts well, then cut in half. Break up about one-third of the sprouts into leaves, then divide the Brussels sprouts evenly between the three jars.
Bring the vinegar, water and Maldon salt to a boil in a large pot over a medium-high heat for about 5 minutes, until the salt is dissolved. Add the sliced garlic and spices and stir.
Pour the vinegar mixture into the jars, filling the jars to within 1cm of the top. Screw on the lids and leave for two days before eating.