Vanilla Custard

Instructions

1. Prepare the milk mixture
   In a medium saucepan, combine the milk and cream (if using). If using a vanilla bean, scrape the seeds into the milk and add the pod as well. Heat over medium-low heat until steaming but not boiling, about 5 minutes. Remove from heat and let steep for 10 minutes if using vanilla bean. Remove vanilla pod.
2. Whisk the egg mixture
   In a medium bowl, whisk together the egg yolks, sugar, salt, and cornstarch (if using) until smooth and pale yellow, about 2 minutes. The mixture should thicken slightly and ribbon when you lift the whisk.
3. Temper the eggs
   Slowly pour about 1/2 cup of the hot milk mixture into the egg mixture while whisking constantly. This prevents the eggs from curdling. Gradually add the remaining milk, continuing to whisk.
4. Cook the custard
   Pour the mixture back into the saucepan. Cook over medium-low heat, stirring constantly with a wooden spoon or heatproof spatula, until the custard thickens enough to coat the back of the spoon, about 5-8 minutes. Do not allow it to boil, as this will curdle the eggs.
5. Test for doneness
   The custard is ready when you can draw your finger across the coated spoon and the line remains clear. Alternatively, it should reach 170-175°F (77-80°C) on an instant-read thermometer.
6. Strain and flavor
   Immediately strain the custard through a fine-mesh sieve into a clean bowl to remove any lumps. If using vanilla extract instead of a bean, stir it in now. Place the bowl in an ice bath and stir occasionally until cooled.