Ingredients

  • 6 tablespoons (about) olive oil
  • 1 teaspoon minced fresh rosemary
  • 4 very large portobello mushrooms, stemmed, dark gills removed, caps thinly sliced
  • 8 1/2-inch-thick slices country white bread (each about 3x6 inches)
  • Dijon mustard (optional)
  • 8 ounces Fontina cheese, thinly sliced
  • 2 bunches arugula or 1 bunch trimmed watercress

Method

  • Heat 4 tablespoons oil in heavy large skillet over medium-high heat.
  • Add rosemary and stir 30 seconds.
  • Add mushrooms.
  • Cover skillet and cook until mushrooms are tender, stirring often, about 8 minutes.
  • Season mushrooms to taste with salt and pepper; transfer to plate.
  • Wipe out skillet.
  • Arrange 4 bread slices on work surface; spread with mustard, if desired.
  • Top bread slices with cheese, then mushrooms and arugula, dividing equally.
  • Top each with bread slice; press to compact.
  • Brush tops lightly with oil.
  • Heat reserved skillet over medium heat.
  • Place sandwiches, oiled side down, in skillet.
  • Brush tops lightly with oil.
  • Cover and cook until golden on bottom, occasionally pressing with spatula, about 5 minutes.
  • Turn sandwiches over.
  • Cover and cook until golden on bottom and cheese is melted, about 5 minutes longer.
  • Transfer sandwiches to plates; cut in half and serve.