Sourdough bread.
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"You don't want to choose a bread that's super dense or something that's not going to get crisp," Laura Werlin told Insider. "Sourdough is my go-to bread for grilled cheese sandwiches. It's the most versatile and keeps it interesting. Texturally, it's got all these little nooks and crannies that allow the butter, oil, or mayonnaise to really crisp up."
"You want to get the ratio of bread to cheese right, and you're not going to get that if your bread is too thick," she continued. "A half-inch slice of bread is what I recommend."
"What you want to be careful of is choosing a bread that has sugar in it," Heidi Gibson said. "If your bread has sugar in it, it will burn more quickly. You're going to be better off with a more rustic bread than a loaf of processed sandwich bread."