Preheat the oven to 400 degrees . Line a 12-cup muffin pan with 1 1/4-inch paper liners. In a bowl, whisk the flour, baking powder, bittersweet chocolate, hazelnuts, unsweetened cocoa and salt. In a large bowl, whisk the buttermilk, oil, sugar, chocolate-hazelnut spread and eggs. Add the dry ingredients to the wet mixture and fold until just barely blended.
Divide the batter among the liners (fill about three-quarters); top each with 1/2 tsp. raw sugar. Bake until puffed and golden brown and a toothpick inserted into the center comes out clean, 13 to 17 minutes. Cool in the pan.