Preheat oven to 175C (350F).
Add the melted butter, sugar and eggs to a bowl and whisk until well combined. Then add the milk lemon extract, lemon zest and sourdough starter, mixing until well combined.
On top of the wet ingredient mixture, add the all purpose flour, baking powder, baking soda and salt. Lightly whisk the mixture until it forms a batter. You don't want to over mix it here - you don't want a lot of air in this mixture.
Pour the mixture into a buttered loaf pan and bake for 1 hour at 175C (350F).
Remove from the oven and allow to cool in the pan for around 30 minutes before placing on a wire rack to cool completely.
Mix together the powdered sugar and lemon juice until a smooth glaze forms. Drizzle over the cooled cake. Garnish with lemon zest if desired.
