INGREDIENTS
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serves 8 people
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Ingredients
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1 tbsp. unsalted butter
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1 medium bulb fennel, thinly sliced into 1⁄2 inch long pieces (1 cup)
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Salt
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Freshly ground black pepper
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2 tsp. Dijon mustard, plus more for serving
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1 egg, beaten
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1 sheet frozen puff pastry (14 oz.), thawed in the refrigerator (2-3 hours)
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8 oz. very thinly sliced mortadella
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4 oz. shredded fontina (1 1⁄4 cups)