Sift together flour, baking powder, baking soda and salt (if using)
Make buttermilk. add vinegar to milk and let it stand for 5-10 mins. Do not stir.
In a mixing bowl, take butter/oil , sugar and mix till sugar dissolves.
Add yogurt and beat till smooth mix.
Add flour /dry ingredient mix, lightly fold the batter.
Add buttermilk as required to adjust the consistency.
Lightly oil or butter the appe pan with a pastry brush.
With an ice cream scooper or a spoon, carefully transfer batter in the cavities. Fill only half or ¾.
With a small spoon or tsp, add Nutella over the batter. Add as required. Do not add to much.
Cover Nutella with the rest of the batter.
Switch on the gas and keep the appe pan/aebleskiver pan on low heat. Let the donut balls cook for about 2-3 mins.
Flip the balls carefully with a spoon/fork or wooden skewers.
Cook from the other side also. Keep on rotating the donut balls until the batter is cooked from inside. Check with a toothpick. Do not insert the toothpick in the enter ad Nutella will stick
Take out the donut balls from the cavities using spoon, cool completely or enjoy warm with more chocolate syrup/maple syrup or just like that.
Keep in an air tight container, though all the pieces are gone as soon as you serve these ;)!!