1. In a heavy-bottomed saucepan, whisk together sugar, cornstarch, and flour.
2. Slowly whisk in heavy cream, then milk, ensuring even hydration of the starch.
3. In a separate bowl, beat egg yolks lightly. Temper yolks by adding a small amount of warm milk mixture, whisking constantly. Combine yolks back into the pot.
4. Add vanilla bean seeds and pod to the mixture.
5. Cook over medium-low heat, stirring constantly, until the cream thickens and begins to bubble, about 7 to 10 minutes. Avoid scorching.
6. Remove from heat, discard the vanilla pod, and strain the mixture through a fine mesh sieve.
7. Stir in cold cubed butter until fully melted and incorporated.
8. Cover with plastic wrap pressed directly on the surface to prevent skin formation.
9. Refrigerate for at least 3 to 4 hours until fully chilled and set.