Prepare the Oven and Cake Pan: Preheat the oven to 180°C (350°F) for a conventional oven or 160°C (320°F) for a fan-forced or convection oven. Grease a 20 cm (8-inch) cake pan with butter.
Combine the Wet Ingredients: Add the vegetable or canola oil, eggs, lemon zest, fresh lemon juice, plain yogurt, and caster sugar to a large mixing bowl. Whisk until the ingredients are thoroughly combined.
Incorporate the Dry Ingredients: Sprinkle the plain flour, baking powder, and salt over the wet mixture. Whisk until the batter is smooth, allowing a few small lumps to remain if necessary.
Fill the Cake Pan: Pour the batter into the prepared pan. The mixture should be fairly thick but still easy to pour.
Bake the Cake: Place the pan in the preheated oven and bake for approximately 50 minutes, or until a skewer inserted into the center comes out clean.
Cool the Cake: Remove the cake from the oven and take off the pan’s metal ring. Transfer the cake to a wire rack and allow it to cool before applying the glaze.
Prepare the Lemon Yogurt Glaze: Place the icing sugar, lemon juice, and yogurt in a bowl. Whisk until the mixture is smooth. Check the consistency by letting a little glaze run down the side of the bowl. If it is too thick, add more yogurt, 1 teaspoon at a time, until it flows slowly while remaining thick enough to provide an opaque coating. Prepare the Glazing Surface: Place the wire rack over a baking tray or a sheet of baking paper to catch any excess glaze.
Glaze the Cake: Pour the glaze into the center of the cooled cake. Gently guide it toward the edges so that it spreads across the top and drips down the sides.
Allow the Glaze to Set: Leave the glazed cake undisturbed for 1 hour to allow the topping to set before transferring it to a serving plate.
Add Optional Lemon Decoration: For the lemon-slice decoration, cut two thin lemon slices and make a slit from the edge toward the center of each slice. Twist the first slice into shape, place it on the cake, then twist the second slice in the opposite direction and position it overlapping the first.