Blue Cheese Dressing

1/4 cup mayonnaise, try homemade mayonnaise 1/4 cup sour cream 2 ounces (60g) crumbled blue cheese 1 tablespoon minced parsley 1 tablespoon fresh lemon juice, optional Pinch fine sea salt Pinch fresh ground pepper Milk, buttermilk, or water to thin out the dressing, optional In food processor