Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish.
In a large bowl, whisk together the flour, 1 cup of sugar, 0.5 cup cocoa powder, baking soda, and salt for the batter.
In a separate bowl, combine the milk, vegetable oil, and vanilla extract. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Pour the batter evenly into the prepared baking dish.
In a medium bowl, whisk together the 1 cup of sugar and 0.5 cup cocoa powder for the sauce.
Gradually whisk in the hot water until smooth. The sauce will be thin.
Carefully pour the chocolate sauce evenly over the batter in the baking dish. The sauce will sink to the bottom, creating a fudgy layer.
Bake for 30-35 minutes, or until a toothpick inserted into the cobbler (not the sauce layer) comes out with moist crumbs.
Let the cobbler cool slightly before serving. It's best served warm with vanilla ice cream or whipped cream.
Notes
This is a classic "dump cake" style cobbler where the magic happens as it bakes, creating separate layers of cake and fudgy sauce.