Irish Soda Bread

INGREDIENTS

• 4 tablespoons (1/2 stick) cold unsalted butter, cut into 1/2-inch dice
• 1 teaspoon grated orange zest
• 1 3/4 cups cold buttermilk, shaken
• 1 cup dried currants
• 4 tablespoons sugar
• 1 teaspoon baking soda
• 1 extra-large egg, lightly beaten
• 1 1/2 teaspoons kosher salt
• 4 cups all-purpose flour, plus extra for currants