Broiled Mushroom, Red Onion, and Arugula Sandwiches on Country Bread

INGREDIENTS:

• • 1 garlic clove
  • 2 ounces roasted red pepper from a jar, drained
  • ½ cup mayonnaise
  • 1 tablespoon Dijon mustard
  • 1 tablespoon fresh lemon juice
  • Scant ¼ teaspoon cayenne
  • ½ cup freshly grated Parmigiano-Reggiano cheese
  • ½ cup extra-virgin olive oil, plus more for brushing
  • Four 4-inch-diameter portobello mushrooms, stems removed
  • Four ¼-inch-thick slices red onion
  • ½ teaspoon salt
  • ¼ teaspoon pepper
  • 8 thick slices good Italian country bread, large enough to hold the mushrooms
  • 2 loosely packed cups baby arugula

INSTRUCTIONS:

1. 1. 1. In a food processor or blender, puree the garlic, red pepper, mayonnaise, mustard, lemon juice, cayenne, and Parmigiano-Reggiano until smooth. With the motor running, add ¼ cup of olive oil in a thin stream until blended and slightly thickened. Set aside.
      2. Preheat the broiler. Line a large rimmed baking sheet with foil. Arrange the mushrooms top sides up on the baking sheet side by side with the onion slices. Brush the tops of the mushrooms and onion slices with olive oil and season with the salt and pepper. Broil the mushrooms and onion slices about 3 inches from the heat for about 10 minutes, until tender and lightly charred in spots.
      3. Lightly brush the bread slices on one side only with the remaining ¼ cup olive oil, then broil, without turning, about 1 minute, until lightly golden on the oiled sides.
      4. Arrange the bread slices on a work surface, toasted side up. Top 4 slices with 1 portobello mushroom, 1 onion slice, and ½ cup arugula leaves each. Spread the roasted red pepper sauce on the remaining 4 slices, close the burgers, and serve.