Wash the potatoes and peel if desired (leaving the peel on adds texture and flavor). Cut into 1/2-inch cubes. Dice the onion, celery, and carrot, and mince the garlic. Thinly slice the cold bacon with a sharp knife.
In a large pot over medium heat, cook the bacon to your desired crispness, about 6–10 minutes. Remove with a slotted spoon and drain on a paper towel-lined plate. Set aside.
Drain all the bacon fat except 3 tablespoons. Pour the fat into a foil-lined bowl, then wipe the pot. Measure 3 tablespoons of fat from the bowl and return it to the pot. Discard or save the foil for later use.
Add onion, celery, and carrot to the pot and sauté over medium heat for 5–7 minutes, stirring frequently. Add garlic in the last 30 seconds. Add diced potatoes and toss to coat. Stir in 1/2 teaspoon each of salt and pepper, along with thyme, oregano, and cayenne pepper. Toss to coat and cook for 1 minute.
Cover with chicken stock and bring to a boil. Reduce heat and simmer for about 10 minutes, or until potatoes are tender. See note 1 for crockpot instructions.
Mash some of the tender potatoes with a potato masher, leaving some chunks.
In another pot, melt butter over medium heat. Slowly whisk in the flour until smooth and cook for 1 minute. Gradually add 2 cups (463g) of milk, whisking until thickened. Add remaining 2 cups (463g) of milk, whisking until thickened again. Season with salt and pepper (I add 1/2 teaspoon of each, but adjust to taste).
Pour the cream mixture into the soup and stir until thickened, about 5 minutes. Reduce heat to low and stir in the sour cream, chives or green onions, 2 cups (193g) cheese, and half the bacon. Stir until the cheese melts.
Top each bowl with 1/2 cup of the remaining cheese, the remaining bacon, and additional chives or green onions if desired. Enjoy warm!
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Notes
Note 1: To prepare this potato soup in the Crock-Pot (6-quart): Follow steps 1–5, then put everything in the Crock-Pot (except the cooked bacon). Cook on low for 5–7 hours or high for 3–4 hours. Mash the potatoes in the crockpot, then continue with step 7. Add everything to the crockpot and cover for 15–20 more minutes on high to heat through, then serve.Storage: Because this potato soup is cream-based, it is not a great candidate for freezing. Reheat leftovers in a pot, slowly increasing the heat while stirring frequently. Boiling the soup at a high temperature will likely cause the ingredients to separate or even curdle.