Whip the egg whites with stevia to make meringue / Whip the egg yolks with vanilla extract and salt / Steam and mash the sweet potatoes until soft / Combine all ingredients and bake at 170°C for 25 minutes.
Steam the sweet potatoes, peel them, and mash well.
Mix the egg yolks and sugar evenly.
Add mashed sweet potatoes and milk, then mix together.
Sift in cake flour and baking powder, and blend.
Whip the egg whites with sugar to make meringue, then fold into the batter.
Pour the batter into a mold and bake in a preheated oven at 170°C for 30 minutes.