In a small bowl, combine the dry ingredients.Beat all wet ingredients in separate large bowl, adding and beating the buttermilk last. Carefully fold in the flour in 3 batches just until combined.Fill half full with the batter, put in 1 teaspoon Nutella, and add more batter on top to fill the muffin tin to just a little over 3/4 full.Bake for 16-18 minutes or until a toothpick inserted into the center comes out clean. Place the muffin pan on a cooling rack and allow it to cool for 5 minutes before removing the muffins.
To make the crumb topping, place all ingredients in a small bowl and use your fingers to combine until the mixture resembles coarse wet sand. Evenly sprinkle the crumb topping over each muffin.Makes 12 muffins.