Orange Muffins without Butter

I always feel disheartened doing folding method (the cake usually don't rise well) but I have decided to give it another try on these Orange Muffins. I was also attracted with this recipe that does not use butter and indeed the texture was fantastic! I have succeeded with the folding this time and the muffins were light, spongy with a strong orange aroma.  

Ingredients

3 egg yolks
30g Sugar
35g fresh orange juice
Orange zest from one large orange
70g natural yoghurt
80g plain flour
10g corn flour
1/2 tsp baking powder
A pinch of salt

3 egg whites
70g sugar

Directions

1. Beat egg yolks and sugar until white at medium speed and add orange juice, natural yoghurt and mix well.
2. Remove bowl from machine, add in sifted flour (plain flour, corn flour & baking powder) and mix well with a hand whisk, follow by orange zest, mix well again.
3. Whisk egg whites and sugar until peak form.
4. Fold 1/4 of egg white to egg yolk mixture with a rubber spatula until well mix and fold in remaining egg white in two batches.
5. Scoop batter into muffin liners to 3/4 full and place them on a baking tray.
6. Bake at preheated oven at 170C for about 25-30 minutes or until skewer inserted comes out clean.
7. Bang the baking tray together with the small cakes on the counter top 2-3 times once they are cooked, as this will prevent the cakes shrink. Leave to cool and store them in an airtight container in room temperature for 2-3 days.