To make the lemon syrup, place the lemon, water and sugar in a small saucepan over low heat and stir until the sugar is dissolved. Increase heat to high, bring to the boil and simmer 4-5 minutes until the syrup is thickened slightly. Set aside.
Preheat the oven to 180c. Place eggs, sugar, lemon rind and juice in a bowl and whisk to combine. Add the flour and baking powder and mix to combine. Spoon into 2×12 hole lightly greased madeleines tins and bake for 8-10 minutes or until puffed and golden. Turn out onto a wire rack to cool. Drizzle with the lemon syrup to serve.