Steps
1. Rinse the Belgian endive and apple thoroughly.
2. Slice the endive lengthwise into thin strips.
3. Core the apple and slice it thinly.
4. In a small bowl, whisk together the olive oil, Dijon mustard, apple cider vinegar, salt, and pepper to create the vinaigrette.
5. In a salad bowl, combine the sliced endive, apple, toasted walnuts, and crumbled blue cheese.
6. Drizzle the vinaigrette over the salad and toss gently to combine.
7. Serve immediately.