Fruit Tart Pastry Cream

1. Heat the milk:
Pour the milk into a saucepan and heat over medium-high heat. If you’d like to flavor the pastry cream, you can add lavender, cinnamon, or another spice at this stage.
2. Mix the egg yolks and sugar:
In a separate bowl, combine the egg yolks and sugar and mix immediately. Don’t whisk for too long.
3. Add the cornstarch:
Add the cornstarch to the egg yolk and sugar mixture. Mix until the cornstarch is completely dissolved and smooth.
4. Temper the eggs:
When the milk is warm but not yet simmering, add a small amount of the warm milk to the egg mixture while whisking. This gently brings the eggs up to temperature.
5. Combine with the milk:
When the milk is almost at a boil, gradually add the egg mixture to the saucepan while whisking continuously.
6. Cook until thickened:
Continue whisking as the mixture thickens. Whisk quickly if needed, and reduce the heat if the mixture is cooking too aggressively.
The important part is to cook the cornstarch properly. Once the pastry cream has thickened, continue cooking and whisking for a few more minutes to make sure the cornstarch is fully cooked.
7. Cool slightly:
Remove from the heat and allow the pastry cream to cool down slightly. Whisk it from time to time as it cools.
8. Add the butter:
The pastry cream should not be hot/warm when you add the butter. Once it has cooled (you can touch the saucepan to check this), add the softened, cubed butter and whisk quickly and vigorously until completely incorporated and smooth.
9. Chill:
Place plastic wrap directly on the surface of the cream to prevent a skin from forming. Refrigerate until chilled.