For the onion muffins, grease muffin tin and chill. Preheat oven to 200 °C.
Peel and finely dice the onion. Beat egg until thick and creamy. Mix with oil and buttermilk until smooth. Beat in diced onion and 3/4 of the cheese. Sift baking powder, flour, whole wheat flour and baking soda on top and stir into the mixture.
Fill the wells of the pan 2/3 of their height with batter and sprinkle with the remaining cheese.
Bake the onion muffins for 15-20 minutes and then let cool for 10 minutes.
Preparation Tip:
Use whole wheat flour for onion muffins!