- Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment paper, leaving an overhang for easy removal. 
- In a large mixing bowl, whisk together the melted butter, sugar, eggs, and vanilla extract until smooth and glossy. 
- Sift in the flour, cocoa powder, salt, and baking powder. Stir until just combined. Fold in chocolate chips. 
- Pour half the batter into the loaf pan, then drizzle half the hot fudge sauce over it. Swirl gently with a knife. Repeat with the remaining batter and fudge. Bake for 45–50 minutes, or until a toothpick comes out with moist crumbs (avoid overbaking for a fudgy texture). Let cool before slicing.