Preheat the oven to 180 ° top / bottom heat.
First mix the flour, sugar, baking powder and salt together.
Then add the sparkling water, oil and lemon zest and stir briefly to form a dough.
But don't stir too long so that the sponge cake stays nice and loose afterwards.
Now give a greased cake base form and bake for about 20 minutes.
Always use a stick test to check whether the dough is through.
If nothing sticks to the toothpick or wooden stick, the biscuit is ready.