Cook the bacon and pasta: Cook the bacon in a skillet over medium heat until crisp, about 8 minutes, then drain on paper towels and crumble once cool. Meanwhile, cook the pasta in salted boiling water until just shy of al dente a minute less than the package says, since it will continue cooking in the oven. Drain and set aside.

Preheat the oven to 375°F and lightly grease the baking dish.

Build the roux: In a medium saucepan, melt the butter over medium heat, then whisk in the flour and cook for 1 minute, until it smells lightly toasted and no longer raw.

Add the broth and milk gradually: Slowly whisk in the chicken broth, followed by the milk, whisking constantly to avoid lumps. Continue cooking for 4–5 minutes, until the sauce thickens enough to coat the back of a spoon.

Finish the sauce base: Remove from heat and stir in the sour cream, garlic, and half the ranch seasoning (1 tablespoon). Season with salt and pepper, keeping in mind the bacon and cheese will add saltiness too.

Combine and bake: In a large bowl, toss the cooked pasta, shredded chicken, half the crumbled bacon, and half the cheddar (1 cup) with the sauce until evenly coated. Transfer to the prepared baking dish, top with the remaining cheddar, and bake uncovered for 20–25 minutes, until bubbling at the edges and golden on top.

Stir in the second dose of ranch seasoning after baking don’t skip this: Once out of the oven, sprinkle the remaining 1 tablespoon of ranch seasoning and the fresh chives over the top and gently fold them into the top layer. This step matters because dried herbs and seasoning blends lose a noticeable amount of brightness after sitting in a hot oven for 20+ minutes adding a fresh dose at the end brings that sharper, herby ranch flavor back instead of leaving the whole dish tasting flat and one-note.

Top with remaining bacon and serve: Scatter the reserved bacon over the top just before serving so it stays crisp instead of softening under the cheese.