To toast the walnuts preheat the oven to 325°F. Bake the walnuts on a baking sheet for 8 - 10 minutes watching carefully to make sure they don't burn.
Toss the diced apple with the lemon juice. In a large, deep, wooden bowl, toss the apple, spinach, curly endive and escarole. Cover with a kitchen towel and chill until you are ready to serve it.
Whisk together the sour cream, heavy cream, walnut oil, mustard, vinegar, sugar and salt. Taste and correct the seasoning. Add salt and pepper to taste if desired. Pour the dressing over the salad mixture and toss gently to combine.
Top with crumbled cheese, toasted walnuts and the dried cranberries.