Farmers' Market Salad

In a salad bowl, whisk together 1/2 cup extra-virgin olive oil, 3 tablespoons sherry vinegar, 1 1/2 teaspoons Dijon mustard, and 1 teaspoon minced shallot. Add 4 quarts rinsed and crisped salad greens; 2 cups red flame grapes, cut in half; 1 cup toasted walnut halves; and 1 cup crumbled blue cheese (3 oz.) such as Point Reyes. Mix gently to coat, adding salt and pepper to taste.