Prep the Pot: Place the chicken, tomatoes, onion, diced jalapeƱos, butter, taco seasoning, and salt into your Instant Pot or slow cooker. Pour the chicken broth over all the ingredients.
Cook to Perfection (Instant Pot Method): Seal the lid, make sure the vent is set to seal, and use the "Soup" function for 20 minutes. Allow the pressure to release naturally for 15 minutes before opening.
Cook to Perfection (Slow Cooker Method): Cover with the lid and cook on low for 6 to 8 hours, or on high for 3 to 4 hours, until the chicken is tender.
Creamy Finish: Once cooked, carefully remove about 1 cup of the hot broth into a separate bowl. Whisk the sour cream (or Greek yogurt) into this broth until smooth, then stir this creamy mixture back into the main pot.
Shred & Serve: Take the cooked chicken out of the pot and shred it using two forks (or a hand mixer for super quick shredding!). Return the shredded chicken to the soup. Taste and adjust seasonings if needed.
Enjoy! Serve your delicious soup hot, perhaps topped with fresh cilantro, sliced avocado, or a sprinkle of cheese.