Instant Pot Instructions:

1. Turn Instant Pot to sauté setting. When display says HOT add in the butter and let it melt. Add in the shallot and celery and sauté for 2-3 minutes.
2. Pour in the broth and scrape bottom of pot so that nothing is sticking. Turn off Instant Pot. 
3. Add in the pepper, garlic powder, vinegar, chicken and pasta.
4. Cover Instant Pot and secure the lid. Make sure valve is set to sealing. Set SOUP button to 1 minute. When time is up move valve to venting. Remove the lid. 
5. Pour some of the hot broth in with the milk to temper and then pour it into the pot. Stir in the parmesan, spinach and sundried tomato pesto.
6. Adjust seasonings to taste. Ladle into bowls and serve. 

Slow Cooker Instructions:

1. In a pan on the stove, melt the butter over medium heat. Add in the shallot and celery and sauté for 2–3 minutes to soften and bring out their flavor. Transfer everything to the slow cooker.
2. Pour in the chicken broth, pepper, garlic powder, vinegar, and chicken. Stir to combine.
3. Cover and cook on low for 4–6 hours or on high for 2–3 hours.
4. Add the pasta during the last 30–40 minutes of cooking time (depending on the shape and your slow cooker’s heat level) and let it cook until tender.
5. Warm the milk slightly and whisk in a bit of the hot broth to temper it. Stir the milk mixture into the slow cooker along with the parmesan, spinach, and sundried tomato pesto.
6. Cover for about 5–10 minutes to let the spinach wilt and the flavors meld.
7. Taste and adjust seasonings as needed, then ladle into bowls and serve.