In a saucepan over low-medium heat, warm milk (do not boil)

In a medium bowl, whisk sugar, flour, and salt

Add egg yolks to flour mixture and combine until it forms a paste

Add some of the warmed milk into the egg mixture and whisk to combine

Continue adding milk to the mixture, whisking to combine

Add mixture back into saucepan

Over medium heat, whisk mixture continuously until it thickens

When bubbles start to form, remove from heat

Strain, if desired

Stir in vanilla

Cover with plastic wrap against the pastry cream to prevent a skin from forming

Chill before serving