Heat the Milk Mixture: Pour 2 cups of whole milk and 2 teaspoons of vanilla bean paste into a medium-sized saucepan. Heat over low-medium heat for about 5-7 minutes until warm.

Prepare the Dry Ingredients: Whisk together 2/3 cup of sugar, 1/4 cup of cornstarch, and 1/4 teaspoon of salt in a mixing bowl until evenly combined.

Whisk in the Egg Yolks: Add 4 egg yolks to the dry mixture and whisk vigorously until pale yellow.

Temper the Egg Mixture: Once the milk is steaming, drizzle half a cup of milk into the egg yolks while whisking. Then, pour the egg mixture back into the saucepan.

Cook the Custard: Cook over medium-low heat, whisking constantly for about 3-5 minutes until thickened.

Incorporate Butter: Remove from heat and stir in 1 tablespoon of unsalted butter until melted and combined.

Cool and Store: Cover with plastic wrap directly on the surface and cool for about 20 minutes, then refrigerate for at least 3 hours.