In a heavy saucepan, whisk together milk, egg yolks and sugar. Split vanilla beans, if using, then scrape out seeds. Add seeds and vanilla pod to the saucepan. (If using vanilla extract this will be added later.)

Cook over medium heat, stirring regularly until custard coats the back of a spoon--about 185 F. If using vanilla extract, add it now.

Strain to remove vanilla bits and any thickened egg, then refrigerate until cool.

Serve with or without a shot of alcohol.