Preheat the oven to 350 (F) and prepare two 8-by-3 inch round cake pans by spraying liberally with cooking spray and lining the bottom of each pan with a parchment paper circle. Spray the parchment circles and set aside.
In a medium heatproof bowl, combine 2 ounces coarsely chopped 70% cacao chocolate and 1 cup BOILING hot chocolate drink. Whisk until the chocolate is completely melted, before allowing the mixture to cool for 15 minutes.
While the chocolate mixture is cooling, whisk together 1 1/2 cups all-purpose flour, 1 1/4 cups natural unsweetened cocoa powder, 1 1/2 teaspoons baking soda, 3/4 teaspoon kosher salt and 1/2 teaspoon baking powder in a medium bowl. Set aside.
In the bowl of a freestanding electric mixer fitted with a whisk attachment, whisk 2 large eggs on high speed until foamy, about 2 minutes. Reduce the speed to the mixer's lowest setting and slowly pour in 1/2 cup vegetable oil. Once all the oil has been poured into the eggs, raise the mixer speed to medium and whisk until fully incorporated, about 1 minute.
Reduce the speed back to its lowest setting and slowly pour the slightly cooled chocolate mixture into the egg mixture, before slowly pouring in 1 cup buttermilk and 1 teaspoon vanilla extract. Add 2 1/4 cups granulated sugar and continue whisking on low speed until the batter is smooth and liquid, about 2 minutes.
Stop the mixer, and use a rubber spatula to scrape down the sides of the bowl. Replace the whisk attachment with a paddle attachment and turn the mixer back on to its lowest speed. Slowly add the dry ingredients (from the 3rd step) about 1/4 cup at a time. Once the dry ingredients have all been added, turn the mixer to medium and beat for 1 minute, no more! Be careful not to overmix — if there are one or two flour streaks or lumps left, you can finish mixing the batter by hand with a rubber spatula. This is a pretty lumpy batter, so don't worry if there are still lumps here and there. Divide the batter evenly between the prepared pans. Bake in the preheated oven for 40 to 45 minutes, or until the tops spring back when lightly pressed and a skewer inserted into the center of each cake comes out clean. Transfer to wire racks and let cool in the pans for about 20 minutes. When the cakes are cool enough to handle but the pans are still a little warm, run an offset spatula around the edge of each cake and invert onto the racks to cool completely before frosting.