Cook Pasta: Bring a large pot of salted water to a boil. Cook elbow pasta 1 minute less than al dente, according to package directions. Drain, toss with a little olive oil to prevent sticking, and set aside. Preheat Oven: Set your oven to 375°F. Lightly butter a 3-quart baking dish and set it aside. Cook Bacon: In a large deep skillet or Dutch oven over medium-low heat, cook diced bacon until crispy. Remove with a slotted spoon and drain on paper towels. Leave about 1 tablespoon of bacon fat in the pan; discard the rest. Season Chicken: Turn the heat to medium. Add shredded chicken and ranch seasoning to the pan. Stir and cook for 2–3 minutes. Transfer to a plate and set aside. Make Roux: In the same pan, melt butter and sauté garlic for 30 seconds until fragrant. Add flour and whisk constantly to create a thick paste. Make Cheese Sauce: Gradually whisk in heavy cream and half and half. Keep whisking until the sauce is smooth. Simmer for 3–5 minutes until thickened. Add Cheese: Stir in Parmesan, and half of the Mozzarella and Cheddar cheeses. Stir until the cheeses are melted and the sauce is creamy. Combine: Add the cooked pasta, ranch chicken, and half the bacon into the cheese sauce. Mix until everything is well combined. Assemble: Pour the mixture into your prepared baking dish. Top with remaining Mozzarella, Cheddar, and bacon. Bake: Bake uncovered for 25–30 minutes, or until the casserole is bubbly and golden brown on top.