Twice-Baked Potatoes with Beef Leftover roast beef dons a new jacket

Ingredients

• • 4 large baking potatoes, washed and pricked with a fork
  • 1 onion, finely chopped
  • 4 oz (115 g) white mushrooms, thinly sliced
  • 2 tablespoons (30 ml) olive oil
  • 1/2 cup (125 ml) frozen peas, thawed
  • 3/4 cup (180 ml) chicken broth
  • 1 1/2 cups (375 ml) cold leftover roast beef, very thinly sliced and cut into strips (about 250g/1/2 lb)
  • 1 cup (250 ml) grated Emmenthal
  • Salt and pepper