Place potatoes in a large pot and cover with cold water. Add a pinch of salt and bring to a boil. Cook for 15–18 minutes until fork-tender. Drain and return to pot to dry briefly.
Add butter, warm milk, and sour cream to potatoes. Mash until smooth with a little texture remaining. Season with salt and pepper and keep warm.
Melt butter in a saucepan over medium heat. Whisk in flour and cook 1–2 minutes. Gradually whisk in warm chicken broth until smooth. Simmer until thickened, 4–6 minutes. Season with Worcestershire sauce, salt and pepper.
Warm shredded chicken in a skillet with a bit of butter and a pinch of salt. Cook and crumble bacon, shred cheese, and slice scallions.
Divide mashed potatoes among bowls, top with shredded chicken, ladle gravy over, then add cheddar, bacon, scallions, and a dollop of sour cream. Garnish and serve immediately.
Notes
Make mashed potatoes and gravy ahead and reheat before assembling.
Use vegetable broth and roasted cauliflower or lentils for a vegetarian version.
To keep potatoes extra fluffy, heat the milk before adding to the potatoes.