Separate the egg whites and yolks.
Add a small amount of lemon juice and erythritol to the egg whites and whip until stiff peaks form.
Mix the egg yolks, milk, and erythritol together.
Add almond flour, baking powder, and cocoa powder to the yolk mixture and mix until well combined.
Fold the whipped egg whites into the yolk batter in three additions.
Pour the batter into a chiffon cake pan.
Bake at 170°C (338°F) for 30-35 minutes.
Let cool, then remove from the pan.