Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In another bowl, mix the milk, vegetable oil, vanilla extract, and egg until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fill each muffin cup halfway with the batter. Add a teaspoon of Nutella to each cup, then top with more batter until the cups are about ¾ full.
In a small bowl, mix together the sugar and ground cinnamon for the topping. Sprinkle this mixture over the tops of the muffins.
Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.