### Instructions:
1. **Preheat & Prep:** Preheat your oven to 350°F (175°C). Lightly grease a 9×13 inch baking dish.
2. **Combine Dry Cake Ingredients:** In a large bowl, whisk together the flour, granulated sugar, ¼ cup cocoa powder, baking powder, and salt.
3. **Add Wet Cake Ingredients:** Pour in the milk, melted butter, and vanilla extract. Stir until just combined. Be careful not to overmix; a few lumps are okay.
4. **Spread Batter:** Pour the cake batter evenly into the prepared baking dish.
5. **Prepare Fudge Topping (Dry):** In a separate small bowl, whisk together the remaining ¼ cup cocoa powder and the brown sugar.
6. **Sprinkle Topping:** Evenly sprinkle the cocoa and brown sugar mixture over the cake batter in the pan. Do not stir it in!
7. **Add Hot Water:** Carefully and slowly pour the 1 ½ cups of hot water over the entire top of the cake, making sure it covers all the dry mixture. Again, do not stir. It will look like a chocolate soup on top, but trust the process!
8. **Bake:** Bake for 30-35 minutes, or until the cake is set and the edges are bubbling. A toothpick inserted into the cake portion (not the sauce) should come out clean.
9. **Rest & Serve:** Remove from the oven and let it cool for at least 15-20 minutes before serving. This allows the sauce to thicken beautifully.
10. **Serve Warm:** Serve warm, scooping generous portions into bowls, making sure to get plenty of that delicious hot fudge sauce from the bottom.
### Short Tips:
* **Quality Cocoa:** Using good quality unsweetened cocoa powder for both the cake and the topping will significantly enhance the chocolate flavor.
* **Don’t Overmix:** Overmixing the cake batter can lead to a tough cake. Mix until just combined.
* **Hot Water is Key:** The hot water is crucial for creating that magical separation of cake and fudge sauce. Don’t substitute with cold or lukewarm water.
* **Serving Suggestions:** This cake is divine on its own, but it’s extra decadent served with a scoop of vanilla ice cream or a dollop of whipped cream.
* **Storage:** Leftovers can be stored covered in the refrigerator for up to 3-4 days. Reheat gently in the microwave for a warm, gooey treat.
