Roast Beef Sandwiches with Lemon-Basil Mayonnaise and Roasted Red Onions

Ingredients

• 6 4x3-inch pieces ciabatta
• 3 large red onions
• 7 tablespoons extra-virgin olive oil
• ¼ cup balsamic vinegar
• 1 cup mayonnaise
• ¼ cup fresh basil
• 1 ½ tablespoons fresh lemon juice
• + 3 more ingredients
• • 2 ¼ teaspoons grated lemon peel
  • 16 ounces thinly sliced roast beef
  • 2 cups arugula

Preheat oven to 425°F. Line large rimmed baking sheet with foil. Gently toss red onions, 5 tablespoons oil and vinegar in large bowl. Sprinkle with salt and pepper. Arrange onions in single layer on prepared sheet. Bake onions until brown at edges and just tender, about 40 minutes. Cool. Mix mayo...

View full recipe at Epicurious