01 -
Preheat oven to 175°C. Lightly grease a 23x33 cm baking dish to prevent sticking.
02 -
In a large bowl, blend Bisquick baking mix, granulated sugar (if using), and a pinch of salt until evenly incorporated.
03 -
In a secondary bowl, whisk together sour cream, lemon-lime soda, melted butter, and vanilla extract (if using). Stir in lemon zest until thoroughly combined.
04 -
Gradually fold the wet mixture into the dry ingredients. Mix gently, leaving some small lumps; do not overwork the batter. The consistency should remain thick and lightly effervescent.
05 -
Transfer batter evenly into the prepared baking dish. Bake for 25–30 minutes, or until the surface is golden brown and a skewer inserted at the centre emerges clean.
06 -
Allow to cool for 10 minutes before slicing into squares. Serve warm. Optionally, sprinkle with powdered sugar or drizzle with honey for enhanced sweetness.