Preheat the oven to 400 °F (205 °C) and grease a 10.5”x15.5” (27 cm x 39 cm) jellyroll pan.
In a large mixing bowl, stir together the sugar, flour, cinnamon and salt.
2 cups (400 grams) granulated sugar, 2 cups (250 grams) flour, 1 teaspoon cinnamon, 1/2 teaspoon salt
In a medium saucepan over medium-high heat, mix together the butter, oil, cocoa powder and water. Bring to a rapid boil, then pour over the dry mixture and stir until combined.
1/2 cup (113 grams) unsalted butter, 1/2 cup (120 ml) canola, 1/4 cup (29 grams) natural cocoa powder, 1 cup (236 ml) water
Stir in the buttermilk, eggs, baking soda and vanilla until combined.
1/2 cup buttermilk, 2 large eggs, 1 teaspoon baking soda, 1 teaspoon vanilla extract
Pour the batter into the greased pan and bake for 20 minutes (start the icing after 15 minutes of baking) or until the edges of the cake pull away from the pan and the center springs back when gently pressed. A toothpick inserted in the middle should come out clean.
Five minutes before the cake is done, prepare the icing.