Preheat the oven to 400°F. Scrub and dry the potatoes, pierce each one with a fork, rub with oil, and sprinkle with salt. Place them on a foil-lined baking sheet.
Bake for 35 to 40 minutes, until a fork slides in with zero resistance and the skins look golden and crinkled. Remove them to a cutting board and let them cool for about 5 minutes.
Add the chopped bacon to a cold Dutch oven and cook over medium heat until crispy, 6 to 8 minutes. Use a slotted spoon to transfer the bacon to a paper-towel-lined plate, leaving every drop of drippings in the pot.
Sauté the diced onion in the bacon drippings over medium heat until soft and translucent, about 5 minutes. Add the garlic and cook for 1 minute until fragrant.
Melt the butter into the onion, then sprinkle the flour over everything. Whisk constantly for 1 to 2 minutes until the roux turns golden, not brown.
Slowly pour in the chicken broth while whisking. Whisk in the milk and heavy cream and bring to a gentle simmer. Cook until the mixture thickens, about 3 to 4 minutes, and coats the back of a spoon.
Scoop the baked potato flesh into the pot. Chop half of the skins into small pieces and stir them in too. Mash or blend to your preferred texture.
Turn the heat to low and stir in the shredded cheddar a handful at a time until fully melted. Remove from heat, let cool for 1 minute, then stir in the sour cream. Season with salt and pepper to taste.
Ladle into deep bowls and top with reserved bacon, extra cheddar, a dollop of sour cream, and a shower of chives or green onions.