INGREDIENTS
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1/4 cup extra-virgin olive oil
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1 medium onion, finely chopped
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1 clove garlic, chopped
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1 small inner stalk celery, chopped
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2 pounds tomatoes, chopped
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1/2 teaspoon sugar
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Kosher salt and freshly ground pepper
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1 cup shredded muenster cheese (about 4 ounces)
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1 cup shredded part-skim mozzarella cheese (about 4 ounces)
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1/2 cup grated parmesan cheese (about 1 ounce)
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8 slices thick sandwich bread
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2 to 3 tablespoons unsalted butter, softened