Creamy Buttermilk Ranch Dressing

3/4 cup mayonnaise
1/2 cup buttermilk
2 tablespoons dried parsley
1/2 teaspoon onion, minced
1 clove garlic, minced
1/4 teaspoon salt
1/4 teaspoon freshly ground pepper
2 tablespoons Parmesan cheese

Mix all ingredients except buttermilk in a small bowl. While stirring, slowly blend in buttermilk. Chill at least 2 hours before using.