Heat a large stockpot over medium-high heat. Add butter. Once melted add onions and cook 3-5 minutes until soft. Then add garlic and cook until fragrant, about 2 minutes.

Add flour and stir to combine—cook for 2 min, mixing every 30 sec. Then add in chicken or vegetable stock slowly, whisking until smooth. Continue to add half-n-half, potatoes, salt, pepper, garlic powder, dried mustard, and thyme. Stir well.

Slowly bring the soup to a low boil—don't let it rapidly boil—then reduce the heat to low, cover, and let simmer for 20 min. Once done, turn off the heat and mix in the cheeses, green onions, sour cream and 1/2 tsp salt. Cover back up and let it sit for 15 minutes to macerate. Serve warm with some crusty bread.