Begin by heating oil and butter in a pan or deep pot over medium heat.
Once the butter is melted, add chopped onion and sauté until soft, about 3-4 minutes.
Next, stir in crushed garlic and cook for 30 seconds.
Add flour, whisking well to create a thick base.
Then, mix in potatoes, broth, milk, cream, salt, pepper, and cayenne, blending until all ingredients are well combined. Bring the mixture to a boil, then reduce heat to low and simmer for 20 minutes, or until potatoes are tender.
Keep the heat low. Carefully transfer half of the soup to a blender, processing until smooth and creamy.
Return this to the pot, adding sour cream and stirring until well mixed.
Continue to simmer for another 10 minutes on low heat.
Serve hot, garnished with grated cheese, chopped green onions, and a sprinkle of chili flakes for an extra kick