Preheat the oven to 350°F (175°C) and grease a small cake pan.
Mix wet ingredients – In a bowl, whisk the egg, salt, and sugar until slightly frothy. Stir in the grated lemon zest (or vanilla sugar), oil, yogurt, and lemon juice until well combined.
Add dry ingredients – Sift in the flour and baking powder, and gently mix until you have a smooth batter. Do not overmix.
Bake – Pour the batter into the prepared cake pan and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
Cool & Serve – Let the cake cool before removing from the pan. Serve plain, dusted with powdered sugar, or topped with fruit and enjoy!