Wash the beets thoroughly under cold water.
Place the beets in a pot and cover them with water.
Bring the water to a boil over medium heat.
Reduce heat and simmer for about 30-45 minutes until tender.
Remove the beets and let them cool.
Peel the skins off the beets and slice them into rounds.
In a saucepan, combine apple cider vinegar, water, sugar, and salt.
Add black peppercorns, minced garlic, mustard seeds, and bay leaf to the mixture.
Bring the mixture to a boil, then reduce to a simmer for 5 minutes.
Pour the hot pickling liquid over the sliced beets in a jar and seal tightly.