Preparation Steps

• Heat oven to 375°F. Lightly grease a 9x13-inch baking dish. Arrange bacon on a sheet pan and bake until crisp, 12–15 minutes; drain and crumble. Reduce oven to 375°F if it climbed during the bacon bake.
• Bring a large pot of well-salted water to a boil. Cook the spaghetti until just shy of al dente (about 1 minute less than package time). Reserve 1/2 cup pasta water, then drain.
• While the pasta cooks, warm the milk in a large deep skillet over medium-low heat. Add the cream cheese and processed cheese; whisk steadily until the sauce is smooth and creamy, 5–7 minutes. Tip: cubing the cheeses helps them melt evenly without scorching.
• Season the sauce with ranch seasoning, garlic powder, and black pepper. Fold in the shredded chicken and half of the crumbled bacon; heat through. If the sauce seems thick, loosen with a splash or two of the reserved pasta water.
• Add the drained spaghetti and most of the chives to the skillet and toss until every strand is coated. Transfer the mixture to the prepared baking dish and scatter the cheddar over the top.
• Bake uncovered at 375°F for 15 minutes, then switch to broil and cook 2–3 minutes until the cheese is spotty and golden. Let the casserole rest for 5–10 minutes so it sets.
• Finish with the remaining bacon and the rest of the chives before serving.