1. Cut up the bacon and add it to a soup pot (I use kitchen shears to make this job easy). Fry the bacon over medium-high heat until it's nice and crispy (about 10 minutes).
2. Meanwhile, prep your onion and potatoes. You can peel the potatoes like I did, or scrub them and leave them unpeeled if you prefer.
3. Once the bacon is done, take it out of the pot and set it aside. I like to leave about half the bacon fat in the pot, about 2 tablespoons or so (it's fine to eyeball it). Discard the rest of the bacon fat or reserve it to use in another recipe.
4. Add the onion to the pot and sauté it for 5 minutes.
5. Stir in the flour and cook it for about a minute.
6.Whisk the milk in slowly until the flour has nicely melted into it and there's no clumps.
7. Add the chicken broth, garlic, and potatoes. Increase the heat to high. Scrape up any brown bits from the bottom of the pot. When the soup is almost boiling, reduce the heat and cover the pot with the lid slightly ajar. Let the soup simmer for 20 minutes (you want it to be simmering fairly gently).
8. While the soup's cooking, get the cheddar, scallions, and sour cream ready.
9. The potatoes should be quite fall-apart tender by now. I like to take my potato masher and mash the potatoes a little bit right in the pot, but if you want to leave the potatoes as-is, that's fine too.
10. Stir in the sour cream and most of the cheddar and bacon (I reserve some to top the soup with). Season the soup with salt & pepper as needed. Top each bowl with the scallions and remaining cheddar and bacon.