Baking tomatoes brings out a concentrated sweet and umami flavor to complement the salty, savory cheeses of the mac and cheese. They also offer a pop of color.
In a recipe on her website, Garten replaces shredded cheese with sliced tomato rounds and butter-soaked bread crumbs, creating a well-balanced sweet and savory flavor.
You can use any kind of fresh tomato you'd like. Sliced cherry tomatoes can add sweetness, while multi-colored heirloom tomatoes give the dish a striking look.