To make the dressing, in a blender, combine the Parmesan, buttermilk, olive oil, vinegar, lemon zest and juice, and garlic and blend on high speed until combined, about 30 seconds. Add the sour cream and a generous amount of pepper and blend on high speed for 30 seconds. Season to taste with salt. Set aside.
To make the salad, bring a saucepan three-quarters full of salted water to a bo