Begin by washing and dicing the potatoes into bite-sized pieces. In a large pot, bring enough water to a boil to cover the potatoes completely. Cook until fork-tender, about 15–20 minutes, then drain and set aside.

In the same pot, combine chicken stock, cold water, and diced sweet yellow onion if using. Season with salt and pepper. Bring to a gentle simmer over medium heat for about 20 minutes.

In a separate saucepan, melt butter over medium heat. Gradually whisk in flour, stirring until smooth. Cook for about 2–3 minutes until light golden, then remove from heat.

Slowly pour the roux into the simmering mixture, whisking to prevent lumps. Stir in heavy whipping cream and simmer for an additional 20 minutes.

Gently fold the cooked potatoes into the thickened soup base, ensuring even distribution, and let sit for a few minutes to enhance flavor.

Ladle the soup into bowls and top with cheddar cheese, crumbled bacon, and diced green onions. Serve hot.