Preheat the oven to 375°F.
Tear off and discard the tough outer leaves of the cabbage. Cut it in half and cutout its core. Slice the halves crosswise into a fine chiffonade.
Toast the walnuts in the oven for 8 minutes. While they are still warm, first rub them in a clean dishtowel to remove some of the skins, then chop or coarsely crumble them.
To prepare the dressing, mix the vinegar with the lemon juice, some salt, and a generous amount of pepper.
Whisk in the olive oil and then the creme fraiche or cream. Taste and adjust the acid and salt as desired.
Quarter,peel, and core the apples. Slice the quarters lengthwise fairly thin and cut these slices lengthwise into a julienne. Toss the cabbage, apples, and walnuts(and blue cheese, if you’re using it) with the dressing and an extra pinch of salt. Let the salad sit for 5 minutes, taste again, adjust the seasoning as needed, and serve.
