Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a 13x18-inch sheet pan with non-stick spray.
Mix Dry Ingredients: In a large bowl, whisk together the flour, sugar, baking soda, salt, and cocoa powder until well combined.
Combine Wet Ingredients: In another bowl, combine the vegetable oil, buttermilk, eggs, food coloring, vanilla extract, and vinegar. Mix until all ingredients are well blended.
Mix it Up: Gradually add the wet ingredients to the dry mixture, stirring until smooth and combined.
Pour and Bake: Pour the batter into the prepared sheet pan and spread it evenly. Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Cool the Cake: Remove the cake from the oven and let it cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
Frost the Cake: For the cream cheese frosting, beat the softened butter and cream cheese in a bowl until creamy and smooth. Gradually add in the powdered sugar and vanilla extract until well combined. Frost the cooled cake generously.
Slice and Serve: Cut into squares, serve, and enjoy every delicious bite!