Preheat the oven to 180c 350f. Butter and baking paper are used to grease a 20 cm square cake pan. Set it aside.
Combine the sugar and melted butter. Add the eggs, vanilla, and lemon zest. Mix in the flour and continue to mix until well combined.
Spread the mixture evenly in the prepared tin. Now Bake the cake for 30 to 35 minutes, or until it is golden brown. Let the cake cool completely.
To make the raspberry icing, heat the jam in a microwave for 30-60 seconds. Strain the jam into a bowl. It should be set aside.
Mix the melted jam and icing sugar. Mix in the water 1 teaspoon at a time. Continue mixing until the icing becomes smooth but still a bit fluid.
After the cake cools, take it out of the tin. Peel off the baking paper. Now Place the cake on a wire rack and place a baking sheet underneath. Spread the icing on the cake and then quickly cover it with it.
Before you cut into squares, let the icing set. Serve.