INGREDIENTS
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3tablespoonsolive oil, plus more for the grate
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1/2cupchopped cornichons
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1tablespoonchopped capers
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1teaspoonred wine vinegar
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kosher salt and black pepper
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8portobello mushrooms (about 3 pounds total), stems discarded
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4ouncesfontina, sliced
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4ciabatta rolls, split
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4leaves romaine lettuce