INGREDIENTS
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6 ounces unsweetened chocolate (100 percent cacao), chopped
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3 sticks (1 1/2 cups) unsalted butter, cut into pieces
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3 cups sugar
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6 large eggs
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1 tablespoon pure vanilla extract
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1 teaspoon fine sea salt
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1/2 cup unsweetened cocoa powder (any type, as long as it’s unsweetened)
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1 cup all-purpose flour
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Maldon sea salt, if desired
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EQUIPMENT: an 18- by 13-inch rimmed baking sheet (a.k.a. half-sheet pan)