Preheat the oven to 350°F. Generously spray an 8x8 inch baking dish with nonstick cooking spray and set it aside.
In a medium bowl, whisk together the flour, 0.67 cup granulated sugar, 0.33 cup cocoa powder, baking powder, and salt until combined.
Whisk in the half and half, vegetable oil, and vanilla extract until just combined.
Evenly spread the cake batter into the prepared baking dish.
In a small bowl, whisk together 0.5 cup granulated sugar, brown sugar, and 4 tablespoons cocoa powder.
Sprinkle the sugar and cocoa mixture evenly over the cake batter.
Pour the boiling water over the dry sugar mixture. Do not stir. Bake for 30 to 35 minutes. Remove from oven and allow to rest for 15 to 20 minutes before serving.
Notes
Serve warm with vanilla ice cream for extra indulgence. The pudding layer is wonderfully fudgy and pairs perfectly with the moist chocolate cake on top.