Step 1: Preheat your oven to 325°F (160°C). Grease and flour a 10-12 cup bundt pan or a 9x13 inch baking pan thoroughly. Tap out any excess flour.
Step 2: In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
Step 3: In a large mixing bowl, combine the brown sugar, granulated sugar, vegetable oil, and vanilla extract. Beat with an electric mixer until well combined.
Step 4: Add the sour cream and eggs to the sugar mixture. Beat on medium speed until just smooth and creamy, scraping down the sides of the bowl as needed.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Step 6: Carefully pour in the hot coffee (or hot water) and mix on low speed until the batter is smooth. The batter will be thin.
Step 7: Pour the batter into your prepared pan. Bake for 60-70 minutes, or until a wooden skewer inserted into the center comes out clean. Baking time may vary depending on your oven and pan type.
Step 8: Let the cake cool in the pan for 15-20 minutes before inverting it onto a wire rack to cool completely. Serve plain or with your favorite toppings.