Thoroughly trim the mushrooms. Keep whole or slice, depending on the size of the mushrooms.
Peel and halve the garlic.
Rinse, trim, and slice the scallions into pieces 8 cm (approximately 3 inches) long.
Bring the vinegar, sea salt, bay leaves, rosemary, peppercorns, juniper berries, mustard seeds, and 400 ml (approximately 14 ounces) of water to a boil. Add the scallions and mushrooms and simmer for 5 minutes. Fill the mixture into the prepared jars. The mushrooms should be completely covered with liquid. Seal tightly and turn upside down to cool slightly. Turn right side up and cool completely.