In a medium bowl, whisk together mayonnaise, white vinegar, and vegetable oil until smooth and well combined.
Add corn syrup, Parmesan cheese, Romano cheese, and lemon juice to the mixture and whisk until fully incorporated.
Stir in garlic salt, Italian seasoning, parsley flakes, salt, and black pepper until evenly distributed.
Transfer dressing to an airtight container or jar and refrigerate for at least 2 hours before serving to allow flavors to meld.
Shake or whisk well before each use. Store in refrigerator for up to 2 weeks.