Infused with seeds scraped from the pod, this version of vanilla pudding has a rich, tempting flavor. A luscious match for tangy rhubarb — baked with more vanilla — or any number of other toppings, it’s anything but plain vanilla.
Whisk together sugar, flour, and salt in a medium bowl; set aside. Pour milk into a medium saucepan; scrape in vanilla seeds, and add the pods. Stir together. Cook over medium heat until tiny bubbles begin to form around edges of pan, about 7 minutes.
Gradually add the milk mixture to the flour mixture, whisking constantly. Transfer the milk-flour mixture to the saucepan; cook over low heat, whisking constantly, 5 minutes.
Put egg yolks in a small bowl. Whisk in a small amount of the hot milk-flour mixture. Add yolk mixture to saucepan. Cook over medium heat, whisking constantly, until mixture comes to a boil and thickens, 10 to 12 minutes.
Remove from heat; discard pods. Add butter; whisk until melted. Pass pudding through a fine sieve into a medium bowl, forcing it through holes with a rubber spatula. Cover surface of pudding with plastic wrap to prevent a skin from forming. Let stand at room temperature until slightly cooled, about 30 minutes. Spoon pudding into bowls; pudding can be refrigerated, covered with plastic, up to 1 day.