• Preheat the oven to 350℉ and make sure the oven rack is in the center position. Coat the 11"x15" baking pan with shortening and flour.
• Make the flax egg/buttermilk mixture by mixing together the oat milk, vinegar, and ground flax. Set aside for at least 10 minutes while you are mixing together the other ingredients.
  ⅔ cup oat milk, 2 Tablespoons ground flax, 2 teaspoons white vinegar
• Accurately measure the flour. (See blog post.) In a large mixing bowl, combine the flour, sugar, corn starch, baking soda, and salt. Set aside.
  3 cups all-purpose flour, 2¼ cups granulated sugar, 1 teaspoon baking soda, ¾ teaspoon salt, 1 Tablespoon cornstarch
• In a saucepan, melt the butter-flavored Crisco on medium/high heat. Add the cocoa powder, stirring to combine. While the shortening is melting, boil the water. I boil mine in a microwave-safe measuring cup.
  1 cup butter flavored crisco, ¼ cup cocoa powder, 1 cup boiling water
• Once the Crisco/cocoa powder mixture is melted and smooth, carefully add the boiling water and allow the mixture to boil for 30 seconds - see notes. Turn off the heat and add the vegan buttermilk/flax egg mixture, agave nectar, and vanilla extract.
  2 Tablespoons agave nectar, 2 teaspoons vanilla extract, 1 cup boiling water
• Pour the cocoa/vegan buttermilk mixture over the flour mixture. Stir with a large spoon till smooth and all of the ingredients have incorporated - but don't over mix or your cake will be tough and not as tender.
• Pour the mixture into a prepared sheet pan and bake at 350℉ for 30 minutes before checking. You'll know it's done when it bounces back when lightly touched. If you need another one or two minutes of baking then that's okay. Set the cake on a cooling rack for 30 minutes before making the frosting.

The frosting

• In a saucepan, melt the vegan butter. Add the cocoa, stir to combine, and turn off the heat. Add the oat milk, vanilla, pinches of salt, and powdered sugar. Stir together somewhat aggressively (or use a mixer) to remove the powdered sugar lumps and pour over the (mostly) cooled cake. (See notes.)
  ½ cup vegan butter, 3 Tablespoons cocoa powder, ¼ cup oat milk, 1 teaspoon vanilla extract, 3⅓ cups powdered sugar, 2 generous pinches of salt
• Cool completely and cut into squares, eat. It's a little messy and goopy but oh so tasty! This cake actually improves the next day in flavor and texture.