1. In a medium saucepan, whisk together lemon juice, lemon zest, sugar, cornstarch, and salt over low heat.

2. Slowly whisk in the beaten egg yolks, stirring constantly until the custard thickens.

3. Remove from heat and stir in 2 tablespoons of butter and vanilla extract. Let cool completely.

4. Preheat oven to 350°F (175°C). Grease and line a cake pan.

5. Cream butter and sugar together until light and fluffy.

6. Add eggs one at a time, mixing well after each addition. Stir in lemon zest and vanilla.

7. In a separate bowl, mix flour and salt. Add this mixture to the butter mixture alternately with milk until combined.

8. Pour batter into the prepared pan and smooth the top.

9. Bake for 25–30 minutes or until the center springs back lightly when touched.

10. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

11. Once cooled, slice the cake horizontally into two even layers.

12. Spread the cooled lemon custard over the bottom layer.

13. Place the top layer back on and dust with powdered sugar or more custard as topping.

14. Chill slightly before serving for best results.