In a large pot or Dutch oven, cook the bacon over medium heat until crispy. Remove bacon and set aside, leaving the drippings in the pot.

Add butter to the bacon drippings. Add onion and cook until softened, about 3–4 minutes. Stir in garlic and cook for 30 seconds.

Sprinkle in the flour and stir well. Cook for 1–2 minutes to remove the raw flour taste.

Slowly whisk in the chicken broth, adding enough to just cover the potatoes.

Add the diced potatoes. Bring to a simmer, cover, and cook until potatoes are fork-tender, about 15–20 minutes.

Stir in the milk and heavy cream. Simmer gently until thick and creamy.

Season with salt, pepper, and optional cayenne to taste.