Banana Nutella Muffins

• Preheat the oven to 425°F / 220°C and line a muffin pan with 12 paper liners. Set aside.
• In a large bowl, whisk together 1 ½ cups finely mashed bananas, ½ cup vegetable oil, 2 large eggs, ⅓ cup buttermilk, and 1 teaspoon vanilla extract until combined.
• Sift 2 cups flour, 1 ½ cups sugar, 1 teaspoon baking soda, and ½ teaspoon salt into the wet ingredients. If you don't have a sifter, whisk the dry ingredients together in a separate bowl, then add them to the wet ingredients.
• Add in 1 cup of chopped hazelnuts (optional), then whisk together until just combined and you can no longer see streaks of flour.
• Scoop about ⅔ of the batter evenly between the 12 muffin cups.
• Heat 1 cup of Nutella in the microwave for 15 seconds to make it thinner. Spoon about 2 teaspoon of Nutella on top of each muffin, then top with the remaining muffin batter.
• Drizzle the remaining Nutella over the top of the muffins and swirl it into the batter using a toothpick or scribe.
• Then sprinkle a tablespoon of sanding sugar on top of each muffin to give these muffin tops a nice crunch once they're baked.
• Bake the muffins for 5 minutes at 425°F / 220°C to give the muffins a nice rise, then reduce the oven temperature to 350°F / 175°C. Continue to bake for an additional 14-17 minutes, or until the tops are golden brown.
• Let the muffins sit in the pan for 10 minutes to cool, then move them to a wire rack to finish cooling.
• These can be served slightly warm or at room temperature. Store leftovers in an airtight container at room temperature for up to 3 days.