This classic thick and creamy custard is commonly used as a filling for cakes, tarts, and pastries. It's simple to make and tastes amazing!
Transfer mixture back into saucepan. Cook over medium-low heat, whisking constantly and vigorously so that the eggs won’t curdle, until mixture thickens. Remove from heat and strain using a fine mesh strainer. Transfer to a medium heatproof bowl and add butter, if using. Press a piece of plastic wrap directly onto the surface of the creme patisserie to prevent it from creating a ‘skin’. Cool using a water bath.* Let cool to room temperature, then store in the refrigerator.
Creme patissiere can be covered with plastic wrap and refrigerated for up to 3 days. Whisk before using to get rid of any lumps.
*Using a water bath helps cool the pastry cream quicker and stops the cooking process to prevent any more egg from curdling. To create a water bath, fill a large bowl with a bit of water and ice cubes. Place your bowl of pastry cream inside the larger one so the cold water surrounds the bowl, but does not get inside.