Beat egg yolks and sugar until white at medium speed and add orange juice, natural yoghurt and mix well.
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.
Whisk egg whites and sugar until peak form.
Fold ¼ of egg white to egg yolk mixture with a rubber spatula until well mix and fold in remaining egg white in two batches.
Scoop batter into muffin liners to ¾ full and place them on a baking tray. Cool muffins before serving.
Bake at preheated oven at 170C for about 25-30 minutes or until skewer inserted comes out clean.
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 from too much shrinking.
Recipe by Anncoo Journal at https://www.anncoojournal.com/orange-muffins-without-butter/