Claire Saffitz’s Bûche de Noël Cookies – Cherry Bombe

Ingredients

• FOR THE COATING
• ½ cup/62 grams cacao nibs
• ½ cup/105 grams Demerara sugar
• Generous pinch of kosher salt
• FOR THE DOUGH
• 2½ cups/320 grams all-purpose flour
• 1cup/110 grams powdered sugar
• 3 tablespoons unsweetened cocoa powder
• ½ teaspoon kosher salt (such as Diamond Crystal)
• 12 tablespoons/170 grams unsalted butter, cut into pieces, chilled
• 1 large egg
• 2 tablespoons sour cream
• 2 teaspoons vanilla extract
• FOR FILLING AND ASSEMBLY
• 4 ounces semisweet or bittersweet chocolate, chopped
• 6 tablespoons/85 grams unsalted butter
• 2 tablespoons powdered sugar
• 1 tablespoon all-purpose flour, plus more for work surface
• 1 large egg, yolk and white separated
• 1 teaspoon vanilla extract