Preheat oven to 350ºF. Prepare two 8" pans with butter and flour.
Add oil, sugar and eggs to bowl of mixer. Beat on medium for 2 minutes.
Add melted chocolate chips, Nutella, flour, salt, baking soda, vanilla, hot cocoa mix and 1/2 cup buttermilk . Beat on medium for 1 minute. Scrape down bowl. Add remaining buttermilk and beat for 30 seconds.
Pour batter into pans and bake for 22-35 minutes. The cake is done when a toothpick inserted into the center comes out clean with just a few moist crumbs.
Rest for 10 minutes and then turn out onto wire rack to cook completely.
Make Milk Chocolate Mousse.
To Assemble: cut cake layers in half horizontally to make 4 layers. Place one on a serving platter. Spread with 1/4 of Milk Chocolate Mousse. Repeat 3 times to finish with mousse at top of cake.
Make Glaze. Drizzle Glaze over cake. Top with milk chocolate curls.