Bring a large pot of water to a boil. Add half the salt and cook the penne 1 minute less than the package directions. Reserve 1/2 cup pasta water, then drain.

Meanwhile, cook the bacon in a 12-inch skillet over medium heat for 5 to 6 minutes, until crisp. Transfer it to a plate, leaving the drippings in the skillet.

Pat the chicken cubes dry and season them with the remaining salt and black pepper.

Add the olive oil to the bacon drippings and raise the heat to medium-high. Sear the chicken in one layer for 5 to 7 minutes, turning occasionally, until golden and 165°F inside. Transfer to a plate.

Lower the heat to medium. Add the garlic and ranch seasoning, then stir for 30 seconds.

Whisk the milk, broth, and cornstarch in a small bowl until smooth. Pour into the skillet, scrape up the browned bits, and simmer for 2 to 3 minutes, until the sauce coats a spoon.

Reduce the heat to low and whisk in the cream cheese for 1 to 2 minutes. Remove the skillet from the heat and gradually stir in the cheddar until smooth.

Fold in the penne, chicken, and half the bacon. Add reserved pasta water a tablespoon at a time if needed, then finish with the remaining bacon and parsley.