INGREDIENTS
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14 oz. frozen puff pastry, thawed
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5 tablespoons unsalted butter
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1 1/2 pounds cremini mushrooms, brushed clean and chopped
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2 large shallots, minced
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1 teaspoon kosher salt
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1/8 teaspoon ground pepper
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3 tablespoons all-purpose flour
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2 cups milk, plus more as needed
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2 cups chicken stock
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1 egg, lightly beaten