Combine the mustard with the lemon juice in a bowl and slowly whisk-in the olive oil. Season the vinaigrette to taste with sea salt and freshly ground black pepper.
2 tablespoon lemon juice, ½ teaspoon homemade or Dijon mustard, 3 tablespoon extra-virgin olive oil
Combine the apple and fennel slices in a bowl and pour the vinaigrette over. Season again with freshly ground black pepper if a little bit more punch is desired.
1 fennel bulb, 1 granny smith apple, Sea salt and freshly ground black pepper to taste