Add the bacon pieces to a cold large pot over medium heat. Cook, stirring occasionally, until crisp and browned, about 4 minutes. Transfer to a paper-towel-lined plate with a slotted spoon. Pour off all but 1 tablespoon of the rendered fat.

Pat the chicken pieces dry and season with the salt and pepper. Add to the pot over medium-high heat and sear, turning once, until golden on the outside, about 4 minutes. It will finish cooking in the simmer — don't worry if the centers aren't done yet.

Stir in the garlic and cook 30 seconds until fragrant. Sprinkle in the ranch seasoning and stir to coat. Pour in the chicken broth, scraping up any browned bits, then add the uncooked penne. Bring to a lively boil.

Reduce the heat to medium-low, cover, and simmer until the penne is tender and most of the broth is absorbed, about 10 minutes. Stir twice during cooking so the pasta doesn't stick.

Take the pot off the heat. Add the cream cheese cubes and stir until completely melted and smooth, then stir in the cheddar until melted. If the sauce looks too thick, splash in 2–3 tablespoons of warm broth.

Fold in half the crumbled bacon. Serve in bowls topped with the remaining bacon and a shower of chives.