Start by scooping 12 teaspoons of Nutella onto a wax paper-lined plate or tray. Freeze for 15–20 minutes to firm up while you prep the batter.

Preheat your oven to 375°F and line a 12-cup muffin pan with paper liners.

In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.

In a separate bowl, whisk the sugars, eggs, buttermilk, oil, and vanilla until smooth.

Pour the wet mixture into the dry and gently fold with a rubber spatula until just combined.

Spoon batter into muffin cups, filling each about halfway. Add a frozen Nutella scoop to the center of each.

Top with the remaining batter until muffin cups are ¾ full.

Warm remaining Nutella slightly (about 10 seconds in the microwave) and drizzle ½ teaspoon over each muffin. Swirl with a toothpick.

Sprinkle with sanding sugar if using.

Bake for 16–18 minutes or until the tops are set and a toothpick inserted beside the center comes out clean.

Cool in the pan for 5–10 minutes, then transfer to a wire rack. Serve warm!