Preheat the oven to 350°F (175°C). Grease an 8×4 inch (20×10 cm) loaf pan and line it with parchment paper, leaving an overhang for easy removal.
In a medium bowl, whisk together 1 cup all-purpose flour, ½ cup unsweetened Dutch-processed cocoa powder, 1 teaspoon baking soda, and ¼ teaspoon salt until evenly combined.
1 cup all-purpose flour, ½ cup unsweetened Dutch-processed cocoa powder, 1 teaspoon baking soda, ¾ cup granulated sugar, ¼ teaspoon salt
In a separate bowl, whisk 1 large egg, ¾ cup granulated sugar, ½ cup vegetable oil or melted butter, 1 cup buttermilk, and 1 teaspoon vanilla extract until smooth.
1 large egg, ½ cup vegetable oil or melted butter, 1 cup buttermilk, 1 teaspoon vanilla extract
Add the dry ingredients to the wet ingredients and whisk gently until just combined. Do not overmix. A few small lumps are fine.
Pour the batter into the prepared pan and smooth the top.
Bake on the center rack for 35 –40 minutes, until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the cake cool in the pan for 10 minutes, then remove and transfer to a wire rack. Allow to cool completely before glazing.
Let's make the glaze
For the glaze, gently melt 2.6 oz white chocolate and 1½ tablespoons unsalted butter together in short microwave bursts or over a hot water bath, stirring until smooth.
2.6 oz white chocolate, 1½ tablespoons unsalted butter
Pour the glaze over the cooled cake and sprinkle with Chocolate shavings. Let it set at room temperature for 15–25 minutes before slicing.