Cook 12 ounces bacon in a large deep-sided skillet. Once bacon is crispy, transfer it to a paper towel-lined plate. Remove all but 1/3 cup of the bacon grease from the skillet.
While the bacon cooks, bring a large pot of water to a boil. Add 2 pounds baby red potatoes and cook until fork-tender but not falling apart, about 15 minutes. Drain and set aside to keep warm.
Return the skillet with the bacon grease to low heat. Add 1/4 cup apple cider vinegar, 2 tablespoons granulated sugar, 1/2 tablespoon Dijon mustard, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Bring to a simmer, about 5 minutes.
Add 6 large cloves garlic to the skillet, stir, and cook until fragrant.
Remove from the heat and add the potatoes back to the skillet. Gently fold the potatoes into the dressing to avoid breaking them. Chop the cooked bacon and sprinkle it, along with 1/4 cup fresh parsley over top. Serve warm.
Notes
Potatoes: Use waxy potatoes like baby reds, fingerlings, or Yukon golds.
Make-ahead: Refrigerate for up to 1 day, then refresh with a splash of vinegar or oil.
Vegetarian option: Skip the bacon and use olive oil instead of bacon grease.
Reheating: Warm gently in the microwave or covered in the oven.