Warm the Milk: Pour the whole milk into a heavy-bottomed saucepan and heat over medium until steaming but not boiling, about 5-7 minutes.

Prepare the Egg Mixture: In a bowl, whisk the egg yolks, sugar, cornstarch, and salt until pale and thickened, about 2-3 minutes.

Temper the Eggs: Gradually pour in ½ cup of warm milk into the egg mixture while whisking continuously to avoid scrambling the eggs.

Cook the Custard: Return the mixture to the saucepan over low-medium heat and stir for about 5-10 minutes until thickened.

Add Final Touches: Remove from heat, stir in butter and vanilla extract until butter melts and custard is smooth.

Strain for Smoothness: Strain the custard through a fine-mesh sieve into a bowl to remove any cooked egg bits.

Cool and Chill: Press plastic wrap against custard to prevent skin and cool at room temperature for 15-20 minutes before refrigerating for at least 2 hours.

Serve and Enjoy: Serve chilled or slightly warm with garnishes if desired.