Heat oven to 185°C / 365°F.
Wet mix: Separate egg. Mix egg yolk, yoghurt and vanilla until smooth. Whisk in 90ml of milk.
Dry mix: Mix oat flour, protein powder, baking powder, spice, and salt.
Combine wet and dry ingredients (do not overmix). If batter is too stiff, whisk in 10–20 ml more milk; if loose, add 1–2 tsp oat flour.Fold in grated carrot until just combined. Whisk egg whites until soft peaks. Carefully fold into batter.
Pour into lined/greased form and bake in the oven for 30-35 minutes (depending on oven and form), or until a skewer comes out clean.
Cool and serve. Rest 10 min in pan, then lift out. Top with cream cheese/yoghurt icing or more grated carrots, and enjoy!