1. In a medium saucepan, heat the milk and lemon peel (if using) over medium heat until it is almost boiling. Remove from heat and set aside.

2. In a separate bowl, whisk together the egg yolks and sugar until the mixture becomes light and fluffy.

3. Sift the cornstarch and salt into the egg mixture and whisk until smooth and fully incorporated.

4. Gradually pour the warm milk into the egg mixture, whisking constantly to prevent curdling.

5. Return the mixture to the saucepan and cook over medium heat, stirring continuously with a wooden spoon or whisk.

6. Continue cooking until the cream thickens to a custard-like consistency, about 5-7 minutes.

7. Remove from heat and stir in the vanilla extract or vanilla bean seeds.

8. Transfer the pastry cream to a bowl and cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming.

9. Allow the cream to cool to room temperature, then refrigerate until chilled and set.