Preheat the oven to 170°C (338°F).
Separate the egg yolks and whites.
Mix the egg yolks with milk, protein powder, and oligosaccharide.
Add lemon juice to the egg whites and whip until foamy, then add the sugar in 2-3 additions to make a stiff meringue.
Sift cake flour and baking powder into the yolk mixture and mix.
Fold the meringue into the yolk batter in 2-3 additions.
Pour the batter into a chiffon cake pan and tap it on the counter 3-4 times to remove air bubbles.
Bake in the oven at 170°C (338°F) for 25 minutes.
After baking, invert and let cool completely.