Step 1

In a small saucepan, bring the milk to a boil over medium heat. Meanwhile, whisk egg yolks and sugar together in a small bowl. Add flour, and mix until smooth and free of lumps.

Step 2

Thin egg-yolk mixture with approximately 1/4 cup of warm milk. When remaining milk begins to boil, add it to egg-yolk mixture, and stir well. Return to saucepan, and place over high heat. Cook, whisking constantly, until pastry cream thickens and boils, about 1 minute. (Turning the pan as you whisk helps to easily reach all areas of pan.)

Step 3

Reduce heat to medium, and cook, whisking constantly, until cream becomes shiny and easier to stir, about 2 minutes more. Pour into a bowl, and stir in vanilla. Place plastic wrap directly on surface of pastry cream to prevent a skin from forming, and allow to cool.