Sift your dry ingredients into the bowl of electric mixer. Add the remaning ingredients to the bowl. With paddle attachment on mixer, mix for 2 minutes on medium speed. The batter will be VERY liquidy. Pour into two 9" round pans that have been lined with parchment paper and greased.
Bake for 20 minutes at 350, then rotate the pans in the oven. Bake 15 minutes longer or until a toothpick comes out clean. Cool on wire racks for 20 minutes then gently invert onto racks until completely cool.
For the Frosting:
Cream together butter, cocoa powder and salt.
Scrape down the sides of the bowl and with the mixer on low, mix in powdered sugar while slowly adding milk and vanilla extract. As the sugar incorporates, raise the speed of the mixer to beat the frosting. Beat until smooth.
In a separate bowl, stir together heavy cream and hot chocolate mix. Turn mixer speed to medium and pour cream mixture into frosting in a slow, steady stream, until you’ve reached your desired consistency.
Recipe by Kitchen Meets Girl at https://kitchenmeetsgirl.com/dark-chocolate-cake-with-hot-chocolate-buttercream/