Preheat oven to 350 degrees fahrenheit. Grease a 9×13 pan with cooking spray.
In medium bowl, mix together oil, vinegar and vanilla.
Mix flour, sugar, cocoa, baking soda and salt in a stand mixer.
Add the wet ingredient into the stand mixer and mix until it comes together.
Bring down your speed to low and very slowly pour the hot chocolate into the batter. The batter is going to look very liquidy and that is how it’s supposed to look like.
Bake for 30-40 minutes. Check with a toothpick the middle of the cake to check for doneness. The toothpick should be dry.