6 oz. (3/4 cup) unsalted butter; extra to grease the pans
13-1/2 oz. (3 cups) unbleached all-purpose flour (I recommend weighing it)
¾ cup canola oil
4-1/2 oz. bittersweet chocolate, finely chopped
3 cups granulated sugar
2-1/4 oz. (3/4 cup) natural unsweetened cocoa powder
3 large eggs, at room temperature
¾ cup buttermilk, at room temperature (use milk with a splash of vinegar or lemon juice if you don’t have buttermilk)
2 Tbs. pure vanilla extract
2-1/2 tsp. baking soda
½ tsp. kosher salt

For the frosting
1½ cup butter, softened
6½ cup confectioners’ sugar, more if needed
2 cups cocoa powder
¾ tsp vanilla extract
¾ cup milk