Mussels au Gratin

Ingredients

• • 1 small potato, peeled and diced
  • 1 stalk celery, diced
  • 1/2 cup (125 ml) chicken broth
  • 2 lbs (1 kg) mussels, cleaned
  • 2 cloves garlic, finely chopped
  • 2 tablespoons (30 ml) butter
  • 4 teaspoons (20 ml) unbleached all-purpose flour
  • 1 cup (250 ml) milk
  • 2 tablespoons (30 ml) pesto
  • 1/2 cup (125 ml) arugula, finely chopped
  • Olive oil
  • Salt and pepper