This is tried-and-true family recipe for homemade chocolate cake. The best chocolate sheet cake and the most requested by everyone!
Bring butter, oil, water, and cocoa powder to a boil on the stove.
In a large mixing bowl, combine the sugar, salt and flour. Mix just until combined.
Make a well in the center and add the hot chocolate liquid to the dry ingredients. Mix just until combined.
Add milk, eggs, baking soda, vanilla, and cinnamon. Mix just until combined.
Pour into a greased baking 9 x 13 baking pan and bake at 300 degrees for approximately 30-35 minutes or until cooked through.
As the cake starts to cool, begin making the frosting.
Add butter, cocoa powder, and oil to a pan on low heat.
Add milk, vanilla, and flour mix well and continue to cook on low heat just to cook the flour a bit and make sure everything is combined well.
Remove from heat and add the powdered sugar. Stir until combined, the frosting is completely smooth and powdered sugar is dissolved.
Pour and spread over warm cake. Let cake cool before serving. Serve at room temperature or refrigerated.