Make a restaurant-worthy chicken Caesar with a little help from your humble broiler and sheet pan. Chicken breasts and homemade croutons get golden in the oven. Charring the romaine adds a new dimension to this dinner standby.
Preheat the oven to 450 degrees F. Line half of a rimmed baking sheet with foil, folding up the edges to make a tray. Whisk the anchovies, lemon zest and juice, 1 grated garlic clove, 1/2 teaspoon salt and a few grinds of pepper in a medium bowl; let sit for a few minutes. Stir in the mayonnaise, mustard, 1/4 cup parmesan and 2 tablespoons water. Reserve 2 tablespoons of the dressing in a separate bowl for the chicken. Stir the chives into the remaining dressing.
Mix 2 tablespoons olive oil with the remaining garlic clove; toss with the bread pieces in a large bowl and season with salt and pepper. Spread the bread on the unlined half of the baking sheet. Arrange the chicken on the other half; season with salt and pepper and brush with the reserved 2 tablespoons dressing. Bake until the bread is crisp, about 15 minutes. Remove the croutons to a plate.
Preheat the broiler. Arrange the romaine cut-side up on the open spot on the baking sheet. Drizzle with the remaining 2 tablespoons olive oil and season with salt and pepper. Broil until the lettuce is charred in spots and the chicken is cooked through, 2 to 4 minutes. Let the chicken rest 8 to 10 minutes, then slice.
Divide the lettuce, chicken and croutons among plates. Top with the dressing, the remaining 1/4 cup parmesan and more chives.