Wash all vegetables and pat dry.
Toast walnuts (see tip below). Remove from pan and allow to cool completely before chopping into small pieces.
Thinly slice cabbage and cut apple into matchsticks.
Finely chop shallot.
Heat oil in a large saucepan over medium heat.
Add cabbage, caraway seeds and salt.
Cook, covered, stirring occasionally, until tender, 8 to 10 minutes.
Remove from heat. Add apple, shallot, vinegar, mustard and pepper and stir until combined.
Serve sprinkled with toasted walnuts.