Preheat your oven to 350 degrees and grease two 8-inch cake pans. In a large bowl, beat together the sugar, powdered sugar, softened butter, and canola oil until well combined. Add in the eggs one at a time, beating between each addition, and then add in the vanilla extract until just combined.

In a medium bowl, stir together the flour, salt, baking powder, and baking soda. Add about 1/3 of the mixture into the batter, and beat until just combined. Then add in about half of the buttermilk, again mixing until just combined. Repeat this process until all of the buttermilk and dry ingredients have been added. You should have a fairly thick, smooth batter. Spread evenly into your prepared cake pans, and bake for 30-32 minutes, or until a toothpick inserted into the center comes out with just a few crumbs clinging to it. Cool the cakes for about 5-10 minutes in the pan before turning out and wrapping tightly in plastic wrap to finish cooling.

Chop your dark chocolate into rough chunks and set aside. In a medium microwave safe bowl, microwave the heavy cream for about 2 minutes, or until it is very hot and bubbles are starting to form around the edges of the bowl. Pour in your chopped chocolate, and cover the bowl with a plate or plastic wrap for 5 minutes. Then whisk the mixture until the chocolate is fully combined and you have a smooth mixture. Stir in the vanilla extract and salt. Cover the bowl with plastic, and let the mixture rest at room temperature for about 2 hours, or until it's completely cooled and has a thick and spreadable texture.

Once the cake layers have fully cooled, trim the domed tops off so you have flat, even layers to work with. Frost the cake as desired, using about 1/3 of the frosting for between the layers, and the remaining for the top and sides. Top with sprinkles and slice to serve. Enjoy!