Pickled Oyster Mushrooms and Pearl Onions

Ingredients

• • 1 bag (284 g/10 oz) pearl onions, peeled
  • 1/4 cup (60 ml) olive oil
  • 1/2 lb (225 g) oyster mushrooms, sliced
  • 1/4 lb (115 g) brown mushrooms, cut into quarters
  • 1 teaspoon (5 ml) mustard seeds
  • 1 teaspoon (5 ml) coriander seeds
  • 1 teaspoon (5 ml) fresh rosemary leaves
  • 1/4 cup (60 ml) balsamic vinegar
  • Salt and pepper