Ursula’s breakfast muffins

Preheat the oven to 220 Degrees Celsius.
Mix all the dry ingredients, then add the sultanas, the grated apple or pear and the sweet potato. Mix gently and set aside.
Beat the egg yolk, vanilla essence, oil and sugar together in a large bowl.
Add the dry ingredients, alternating with the milk. mix gently, but thoroughly.
Whisk both egg whites to the soft peak stage and gently fold into the batter.
Spoon the batter into greased muffin pans, slightly overfilling each muffin hollow and place in the hot oven.
Turn the oven temperature down to 180 Degrees Celsius and bake for 20 – 25 minutes.
Insert a skewer in the centre of a muffin to check whether they are cooked.
If there is any raw batter on the skewer, bake for another 5 minutes.