1. Preheat the oven to 350°F and butter a large baking dish.
2. Bring a large pot of salted water to a boil. Cook the pasta until el dente. Drain completely and set aside.
3. While the pasta cooks, melt the butter in a large saucepan. Add the onion and grate in the garlic and cook for 5 minutes, or until the onion is soft. Add the flour, mix well to incorporate, and cook until lightly golden. Slowly whisk in the milk and half-and-half and bring to a gentle simmer. Whisk frequently and cook until thickened enough to coat the back of a spoon.
4. Add in the cheeses and whisk until melted. Season the sauce, to taste, with salt and pepper. Add the cooked pasta to the pot and toss until everything is well coated. Transfer the pasta to the baking dish.

For the Topping:

1. Place the crackers in the bowl of a food processor and pulse until fine crumbs form. Add in the herbs and pulse to combine. With the machine running, slowly stream in the melted butter and run the machine until everything is moistened and crumbly.
2. Top the pasta with the cracker mixture and place the baking dish in the oven.
3. Bake for 30 minutes or until everything is bubbly and gooey and the topping is lightly toasted in spots. Garnish with additional Cheez-it crumbs (I keep these a little coarser for some added texture) and chopped fresh herbs. Serve warm.