In a large bowl whisk together eggs, sugar and cornstarch until sugar dissolves. Set aside.

Place a medium saucepan over medium heat. 

Add in milk, vanilla and butter. Stir to combine.

Bring mixture to a simmer. 

Remove the mixture from the heat. 

Stir in two tablespoons of the egg mixture from the bowl. Whisk it to make sure that it is thoroughly combined.

Return the pan to the heat.

Turn the heat too low. It is very important that this mixture does not begin to boil.

Slowly poor in the egg mixture and whisk continuously until the mixture starts to thicken.  Be sure to slowly add the egg mixture. If you do it too fast it will turn into scrambled eggs. This may take around 15 minutes. The custard should coat the back of a spoon when it is ready.

Poor the custard into dessert cups.

Refrigerate for 4 hours.

Sprinkle nutmeg and cinnamon on top before serving.

Serve cold.