POUR milk into a 2-quart pot. Split vanilla beans in half and scrape out the interior. Put beans and scrapings into the pot (or vanilla extract, if using). Heat over medium-high heat until simmering. Remove from heat. Remove vanilla bean pods. Set aside until ready to use.
MIX SPLENDA® Granulated and cornstarch together in a large bowl. Set aside.
MIX egg yolks together until well blended. Add to cornstarch mixture and stir, using a wire whisk until well blended. Add ½ cup of milk. Stir well.
POUR half of the remaining milk mixture into the cornstarch mixture. Stir well. Pour mixture into remaining milk mixture in saucepan.
COOK over medium heat while stirring constantly with a heat proof rubber spatula until thickened (approx. 2-5 minutes). POUR into heat resistant storage container. Cover and refrigerate until ready to use.