Place the milk and salt into a medium pot and heat over medium heat.
Place the egg yolk, brown sugar, and flour in a separate bowl and whisk together. When the milk starts to simmer, pour a half cup into the egg mixture while whisking it. Temper the egg and add them to the pot with the milk.
Cook over medium heat, whisking constantly, until the mixture thickens and comes to a full boil. Boil for 1 minute.
Remove the pot from the stove and add in the Nutella, stirring until combined.
Pour the hot pudding into the mini pie crusts.
Refrigerate the pies for at least 2 hours to overnight to set.
Whip your cream with a touch of sweetener and top the pies before serving.