Arrange a rack in the middle of the oven and preheat to 325°F. Grease an 8×8-inch square baking pan with nonstick pan spray. Line with parchment paper, leaving some overhang on all sides so it’s easy to lift out the bars after baking, and coat once more with the pan spray. Place the crackers in the bowl of a food processor fitted with the blade attachment. Pulse 20 to 30 times, until the crackers are the texture of coarse sand and no large pieces remain. Add the melted butter and process until the butter is completely absorbed by the cracker crumbs, 15 to 20 seconds. Transfer the mixture to the prepared baking pan and press into an even layer using the bottom of a measuring cup or clean hands. Wipe the food processor out with a paper towel and set it aside. Bake until the crust is light golden brown and very fragrant, 10 to 12 minutes. Let cool slightly. Leave the oven turned on. While the crust is cooling, add the cream cheese, parmesan, sour cream, eggs, milk, garlic, cornstarch, and salt to the empty food processor, and process until completely smooth, 25 to 30 seconds. Pour the mixture over the cooled crust and bake until the filling jiggles slightly when moved but the edges are fully set, 38 to 43 minutes. Turn the oven off, open the oven door halfway, and let the cheesecake cool in the open oven for 30 minutes. (This will help prevent the top from cracking.) Refrigerate the bars uncovered for at least 4 hours and up to overnight. When ready to serve, carefully lift out the bars using the parchment paper and transfer to a cutting board. Cut into 16 pieces (a 4×4 grid), wiping the knife clean between slices. Garnish the tops with the herbs and greens, if using.