SAUTE: Melt butter in a large stockpot or a 6-quart dutch oven. Add the mushrooms and sauté them for 3 minutes over medium-high heat before adding the onions, carrots, and celery. Continue to cook the veggies for an additional 5-7 minutes. Stir in the seasoning mix, garlic powder, dried thyme, mustard, and bay leaves, and give the seasonings a minute to bloom in the heat. Sprinkle the flour over the veggies and stir to coat them evenly; cook the flour for 1 minute so it doesn’t taste raw. Slowly stream in the chicken stock as you whisk the soup to combine. Then add 1 cup of water. When the soup reaches a simmer, add the shredded chicken and dry orzo to the soup, and allow the soup to simmer uncovered for 8 minutes, it’s okay if the orzo isn’t cooked through yet.

FINISH: While the soup is simmering, add sour cream to a small bowl and whisk until smooth. Then, add a tablespoon of the simmering soup to the sour cream as you whisk. Repeat this 3 more times (so it's a total of 4 tablespoons of soup added to the sour cream.) Then, turn the heat all the way down to low on the stove, make sure the soup is no longer boiling. Add the sour cream mixture to the soup, along with the half and half, and allow the soup to heat through gently; about 5 minutes. Taste and make sure the orzo is cooked all the way through, adjust with salt and pepper as needed. It’ll really depend on how salty your chicken stock was. If at any point the soup gets too thick, you can thin it out with additional stock, water, or half and half. Serve warm with bread on the side.