In a large pot, combine the diced potatoes and chicken broth; bring to a boil, then reduce heat and simmer until potatoes are tender, about 10-12 minutes.

While potatoes are cooking, melt butter in a separate saucepan over medium heat; add chopped onion and cook until softened, about 3-5 minutes.

Stir in minced garlic and cook for another minute until fragrant, then whisk in flour and cook for 1 minute to create a roux.

Gradually whisk in milk and heavy cream until smooth; bring to a gentle simmer, stirring constantly, until the mixture thickens.

Once potatoes are tender, mash some of them against the side of the pot with a spoon to thicken the soup, then pour the cream mixture into the pot with the potatoes.

Stir in salt and pepper, and cook for an additional 2-3 minutes, ensuring the soup is heated through but not boiling.

Serve hot, garnished with shredded Cheddar cheese, crumbled bacon, and fresh chives, if desired.