Wash and trim the beets, leaving about an inch of stems.
Place the beets in a large pot and cover with water.
Boil the beets for about 45 minutes until tender.
Remove the beets and let them cool slightly.
Peel the skin off the beets under running water.
Slice the beets into rounds or wedges.
In a separate saucepan, combine apple cider vinegar, water, sugar, and salt.
Add peppercorns, mustard seeds, bay leaf, and garlic to the saucepan.
Bring the mixture to a boil, stirring until the sugar dissolves.
Pour the hot brine over the sliced beets in a jar, ensuring they are fully submerged.