Place black olives, green chiles, chipotle chili powder, oregano, salt and chicken broth in the Instant Pot. Stir to combine and place frozen chicken breasts into the broth mixture.
Lock Instant Pot lid in place making sure the venting valve is sealed.
Cook on high pressure for 3 minutes.
When the cooking time is up, allow the pressure to release naturally for 18 minutes, then do a quick pressure release and when the pressure pin drops, remove the lid.
Remove the chicken from the broth and place on a cutting board. Allow to cool for a few minutes and cut or shred into bite-sized pieces.
Set Instant Pot on "Saute" mode and bring broth to a simmer.
In a small bowl, mix the cornstarch with the sour cream until smooth and whisk into the simmering broth. Whisk until smooth and bring to a simmer. Cook until thickened-- about 1 minute and stir in the chicken and tortilla pieces. Cook for 1 minute longer and turn off the Instant Pot.
Sprinkle cheese over the top of the casserole and cover with the lid until the cheese is melted.
Frozen boneless skinless chicken breasts are best for this recipe. Chicken thighs would also work, especially if you’re making this recipe in a crockpot (they won’t dry out as quickly). Bone-in chicken breasts could add more flavor if that’s what you want to use, but they will take longer to cook.
Weigh your chicken beforehand. If the breasts are larger than 8-10 ounces, follow the chicken cooking guide at the end of this recipe to adjust the cooking time.
Shred the cheese yourself. Pre-shredded cheese has anti-caking ingredients that don't melt as nicely and won’t be as creamy.
Make each bite a bit spicier by stirring in a can of chopped jalapenos or adding several dashes of hot sauce.
Add even more heat with my homemade enchilada sauce. Stir it in when you add the sour cream.
Leftovers store easily in the fridge or freezer. Make sure they’re in an airtight container before storing for a few days in the fridge or for up to a month in the freezer. Reheat on the stovetop or in the oven or microwave.