Heat a large Dutch oven or pot over medium-high heat. Add the butter, oil, onion, and celery. Cook for 4-6 minutes or until translucent. Add the garlic and cook another minute or until fragrant. Stir in the flour and sauté for about a minute to cook it off.

Pour in the chicken stock, and whisk until it is smooth then add the peeled diced potatoes. Bring the soup to a boil, turn the heat down to a simmer, and cover. Cook until the potatoes are tender, about 20 minutes.

Once tender, remove about 1/3 of the potatoes with some stock. Blend until the potatoes are smooth then return to the pot. You can also use an immersion blender and blend some parts of the soup directly in the pot. You want a good mixture of chunky and smooth potatoes.

Add the heavy cream and cheddar cheese and stir until the cheese is melted and the soup is warmed through about 3-4 minutes.

Taste the soup and adjust the seasoning, if desired. Ladle soup into serving bowls and top with a dollop of sour cream, chopped chives or cilantro, and freshly grated cheddar.