• Preheat the oven to 350 degrees
• Prepare an 18x13 inch baking sheet by greasing with butter. Set aside.
• In a medium saucepan, add the water, vegetable oil and cocoa powder and whisk to combine. Heat over medium until the mixture begins to boil. Make sure the cocoa powder is dissolved, then remove from heat and set aside.
• In a large mixing bowl, add the flour, sugar, baking soda and salt. Whisk to combine.
• Pour the hot mixture into the flour mixture making sure to use the spatula to get all the hot mixture out of the pan.
• Use an electric hand mixer (or you can hand whisk yourself) on medium speed to combine the wet and dry ingredients until smooth.
• Add sour cream, eggs and vanilla and mix again until fully incorporated.
• Pour the cake batter into the prepared baking sheet. Use an offset spatula to spread the cake making sure it’s evenly distributed. You can tap the baking sheet on the counter a few times to help it settle.
• Bake for 15-18 minutes or until a toothpick inserted into the center of the cake is clean when removed.
• When the cake has been baked for 10 minutes, begin to make the frosting so that it can be poured onto the cake while it’s still hot.

Make the Frosting

• In a medium saucepan, add the milk, cocoa powder and butter. Heat over medium while whisking constantly so that it doesn’t burn.
• Once the mixture starts to boil, remove it from heat and add the vanilla, salt and powdered sugar. Whisk until fully combined and smooth.
• Pour the frosting over the warm cake and use an offset spatula to help the frosting reach all edges of the cake. I picked up the baking sheet with oven mitts tilted it back and forth to help the frosting become evenly distributed.
• Allow the cake and frosting to set and then cut and serve!