Whisk together egg yolks, almond milk, vanilla and optional sweetener in medium metal bowl.
Slowly mix in the melted coconut oil or butter.
Be sure the oil isn't too hot, or the eggs may cook unevenly.
Place the bowl over a saucepan of simmering water.
Whisk the mixture constantly and vigorously until thickened.
Your instant-read thermometer should register 140°F for 3 full minutes.
Usually, this means about 5 minutes of total cooking time.
(When ready, it should coat the back of a spoon.)
Remove the custard from the water bath.
Serve either warm or chilled.