Preheat oven to 350F degrees. Spray a 9x13-inch baking dish with nonstick cooking spray.
In a large bowl, mix together 2 cups all-purpose flour, 2 cups granulated sugar, 2 teaspoons baking soda, 1/4 teaspoon salt, 1/2 cup unsweetened cocoa, 3/4 cup vegetable oil, 2 large eggs and 1 cup buttermilk until combined well. This part can be done by hand or with an electric/stand mixer.
Once combined, gently stir in 1 cup hot water. This needs to be stirred by hand. If you use an electric or stand mixer, the water may slosh right out of the bowl. Batter will be thin.
Pour batter into prepared baking dish.
Bake for about 35-45 minutes (until it bounces back to the touch or a toothpick inserted comes out clean.)
Allow to cool completely before making frosting.
When cake is cooled, in a medium bowl, with an electric hand mixer, mix together 1/4 cup margarine, 1/2 block (4 ounces) cream cheese, softened to room temperature until smooth.
Then slowly mix in 2 cups powdered sugar along with 1/2 teaspoon vanilla extract until smooth and combined well.
Spread frosting onto cake then sprinkle a few mini chocolate chips evenly on the top. Slice and serve! Keep cake refrigerated .