Preheat your oven to 350°F (175°C) and grease and flour a 10-cup bundt pan.
Combine the flour, the cornstarch, and the baking powder in a small bowl.
Transfer the butter, the sugar and two tablespoons of the flour in a large bowl and beat with a hand-held electric mixer (or with a stand mixer using the whisk attachment). In the meantime transfer the eggs to a jar or small bowl and lightly beat them with a fork.When the butter and sugar mixture is very fluffy and lighter in color, add the beaten eggs gradually, in a thin stream (while beating the batter).Once all of the eggs are added, add the vanilla and the salt.
Stop the mixer and switch to a spatula. Add one third of the flour and mix gently with a spatula. Then, add half of the milk and mix well.Repeat with the other third of the flour, then the rest of the milk and finally the rest of the flour.Add the grated carrot and the sprinkles and mix until just combined. Don't overmix or the cake will be tough.
Pour the mixture in the bundt pan and bake for approximately 50-55 minutes or until a toothpick inserted in the center of the cake comes out clean.Let the cake rest for 10 minutes and invert onto a rack to cool completely.
Make the chocolate cream: Transfer the milk, the hazelnut butter and the chopped chocolate to a saucepan over very low heat and stir until the chocolate melts and the mixture is smooth.Let it cool and thicken a bit, and pour over the completely cooled cake. Sprinkle with some chocolate sprinkles.
Notes
Adding some flour to the butter and sugar mixture will later help the eggs to be mixed into the batter more evenly.A small quantity of cornstarch is used to make the cake more tender.If you skip the ganache, serve this cake with a light dusting of icing sugar