Place bacon in large stockpot over medium heat.
Cook until crispy, then reserve grease, but remove bacon, crumble, and set aside.
To the hot pan and grease, add in celery, carrots, onion, garlic, salt, and pepper.
Cook, stirring often, until the celery and carrots are tender, about 10 minutes.
Reduce heat to low.
Sprinkle in flour, then cook, stirring constantly, for 1 minute.
Slowly whisk in chicken broth.
Pour in half and half and potatoes.
Increase heat back to medium, bring to a simmer, stirring occasionally.
Cover and simmer (you'll probably need to lower the heat back to low) until the potatoes are cooked, about 15 minutes, stirring occasionally.
Remove from heat and slowly stir in sour cream, cheddar, and gruyere until the cheese has fully melted.
Stir in bacon and chicken, taste and re-season, if necessary, then serve with green onions/chives and enjoy!
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