Making Chocolate Pudding from Scratch

Just whipping up some homemade chocolate pudding today. It's easy.
Here's the recipe:
Chocolate Pudding
3/4 cup (150 g) sugar
2 tablespoons (20 g) cornstarch
1/4 teaspoon (1.5 g) salt
5 tablespoons (37 g) cocoa
Mix together dry ingredients in a pot.
1 egg
Mix.
2 cups (475 ml) milk
Mix well.
Warm up on medium heat and stir often.
When it comes to a boil, cook and stir for two more minutes.
Remove from heat and add:
1 tablespoon (14 g) butter
1.5 teaspoons (7 ml) vanilla
Cool for 4-8 hours.
Serve with whipped cream, if desired.