Heat the oven to 400°F. Rub the potatoes with the olive oil and 1/2 teaspoon of the salt, place them on a rimmed baking sheet, and bake for 50–65 minutes, until a knife slides easily into the center.

Melt the butter in a 5-quart Dutch oven over medium heat. Add the onion and cook for 5–7 minutes, until softened.

Stir in the flour and cook for 1 minute.

Gradually whisk in the chicken broth until smooth, then whisk in the milk and heavy cream.

Bring to a gentle simmer over medium heat, stirring often, and cook for 5–8 minutes, until slightly thickened.

Let the potatoes cool for 10 minutes, then halve them and scoop the flesh into the soup.

Add the remaining 1/2 teaspoon salt and the pepper.

Simmer gently for 10–15 minutes, mashing some of the potatoes against the side of the pot to thicken the soup.

Cook the bacon in a 12-inch skillet over medium heat for 8–12 minutes, turning as needed, until crisp.

Drain the bacon on a paper towel-lined plate and crumble when cool enough to handle.

Ladle the soup into bowls and top with the cheddar, bacon, sour cream, and green onions.