Place a 6-quart pot over medium-high heat. Add the bacon and cook, stirring frequently, until the bacon is browned, 6 to 7 minutes. Remove the bacon to a paper-towel lined plate or rack. Pour off all but 3 tablespoons of the bacon fat.
Decrease the heat to medium and add the onions to the pot. Cook, stirring occasionally, until the onion is softened and beginning to brown around the edges, approximately 6 minutes. Add the broth, peanuts, and thyme. Increase the heat to high, and bring to a boil. Once the mixture reaches a boil, reduce the heat to medium-low to maintain a rapid simmer. Cook until the peanuts begin to loosen from their skins and the broth is reduced by one quarter, 20 to 25 minutes.
Turn off the heat and puree the mixture with an immersion blender until smooth. Add the milk, vinegar, salt, and pepper, and puree until combined. Turn the heat back to medium and cook until warmed through, 5 to 7 minutes. Garnish with the reserved bacon and serve immediately.