In a saucepan, add the lemon zest and sugar.
Rub the zest into the sugar until fragrant and slightly moist.
Add the egg yolks.
Whisk in the egg yolks until the mixture is smooth and pale.
Add the cornstarch and salt.
Whisk well until fully combined and lump-free.
Gradually pour in the cold milk, whisking constantly to keep the mixture smooth.
Mix in the lemon juice until fully incorporated.
Add a pinch of turmeric if desired to enhance the color.
Place the saucepan over medium heat and cook.
Stir constantly until the mixture thickens and starts to bubble gently.
Remove from heat and stir in a tablespoon of butter for extra smoothness.
Strain if you want it extra smooth, and divide the pudding into serving dishes.
Cover with plastic wrap touching the surface and chill at least 2 hours.
Before serving, top with whipped cream, lemon zest,, lemon slices and fresh berries if desired.