In a small saucepan, add the sugar, arrowroot, and salt.

Whisk dry ingredients together.

Pour in milk while whisking continuously so the arrowroot powder does not clump.

Over medium heat, whisk continuously until the liquid begins to thicken and comes to a boil (usually about 10 minutes).

Continue to stir briskly for one more minute (this is important because if you don’t go the extra minute it will not be thick enough).

Remove from heat and pour a small amount into a dish with the egg yolks, stir well to combine, and then add back into the pudding.

Stir in butter and vanilla.

Pour into serving dishes.

Let sit for 10 minutes before serving, or cover and refrigerate. A skin may form on top of the pudding when refrigerated, this is normal and completely edible.