Tie the ground nutlets in a cheesecloth packet for easy removal. Heat the cream, half and half, and dried sweet fern nutlets until steaming and cool. When the sauce tastes pleasantly of sweetfern, discard the packet of nutlets.
Meanwhile, bring the maple syrup to a boil and cook for two minutes, then pour into a mixing bowl and allow to cool for a few minutes.
While the syrup is still warm, beat it with the egg yolks until light in color.
Whisk ⅓ of the cream mixture into the egg yolk-maple mix, then whisk in the rest. Transfer the mixture back to a saucepan and cook on low heat, stirring constantly with a spoon, until the mixture barely coats the back of a spoon, about 15 minutes.
It’s important to take your time cooking the crème anglaise, as if the heat gets too hot it will curdle the yolks and make the sauce chunky. Even if you do curdle the yolks though, you can strain it and it will be ok. Chill the sauce completely before serving to give it time to thicken. If you're in a pinch, stir it over a pan of ice.