Why This Recipe Works

Meaty portobellos, buttery fontina, roasted red peppers, and herbed mayonnaise come together for an irresistible vegetarian sandwich. To ensure that the mushrooms are tender, we precook them in the grill pan before assembling and toasting the sandwiches. A grill pan and a Dutch oven (as a weight) mimic the signature marks of a panini press, but a large nonstick skillet can be used in place of the grill pan.

Before You Begin

Use a bread with a sturdy crust here; softer sandwich bread will flatten. You will need a Dutch oven or another similarly heavy pot to press the mushrooms and sandwiches.

Instructions

Whisk ½ cup mayonnaise, 4 minced garlic cloves, and 2 teaspoons minced rosemary together in bowl. In second bowl, toss 6 portobello mushroom caps, halved crosswise; ¼ cup extra-virgin olive oil; ½ teaspoon table salt; and ½ teaspoon pepper together. Heat large grill pan over medium heat for 1 minute. Arrange mushrooms in pan, place Dutch oven on mushrooms, and cook until browned, about 6 minutes per side (cook mushrooms in batches if they won’t all fit). Transfer to plate.

Spread mayonnaise mixture evenly on 1 side of 8 slices crusty Italian bread. Layer 1½ cups shredded fontina on mayonnaise side of 4 bread slices, then top with mushrooms; ½ cup roasted red peppers, sliced; and remaining 1½ cups shredded fontina. Arrange remaining bread, mayonnaise side down, over cheese.

Place 2 sandwiches in pan and place Dutch oven on top. Cook over medium heat until golden brown and cheese is melted, 4 to 6 minutes per side. Transfer to wire rack and repeat with remaining sandwiches. Serve.