Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking sheet and set aside.
In a large mixing bowl, whisk together the sifted flour, sugar, cocoa powder, baking soda, and salt until well combined.
2 cups all-purpose flour
In a saucepan over medium heat, combine vegetable oil, eggs, and vanilla extract. Stir until the mixture is smooth and heated through, about 2 minutes.
2 cups all-purpose flour
Pour the hot mixture over the dry ingredients and stir to combine. Carefully add boiling water, mixing slowly to avoid splashing, until the batter is smooth and thin.
2 cups all-purpose flour
Pour the batter into the prepared baking sheet, spreading evenly. Bake for 30 minutes or until a toothpick inserted into the center comes out with moist crumbs. Allow to cool before frosting.
While the cake cools, make the frosting by melting butter and mixing it with powdered sugar, cocoa powder, vanilla, and milk until smooth and creamy. Spread the frosting evenly over the cooled cake and let set before serving.
2 cups all-purpose flour
