Heat butter and olive oil in a large pot over medium heat.
Add onion and garlic. Cook until soft and translucent.
Sprinkle flour over the mixture and stir well. Cook for 1 minute.
Slowly pour in chicken stock while stirring until smooth.
Add milk and stir until silky.
Add potatoes, garlic & herb seasoning, Italian seasoning, and salt.
Bring to a gentle boil, then reduce heat to low.
Simmer for 40–45 minutes until potatoes are very soft.
Lightly smash some potatoes with a spoon to thicken the soup.
Taste and adjust salt and pepper.
Serve hot with cheddar cheese and desired toppings.