I started by preheating my oven to 350°F (175°C). I lightly greased my loaf pan and lined it with parchment paper, which made removing the bread so much easier after baking.
In a large bowl, I combined melted butter, vegetable oil, granulated sugar, and brown sugar. I whisked it until smooth, then added the eggs one at a time. Finally, I stirred in the vanilla extract, which gave the mixture a warm, sweet aroma.
In another bowl, I whisked together flour, cocoa powder, baking powder, and salt. I slowly added this to the wet ingredients, mixing just until combined. I was careful not to overmix, since that can make the bread dense.
Next, I folded in the chocolate chips. I poured half the batter into the loaf pan, drizzled some warmed fudge sauce, then spread the rest of the batter on top. Using a knife, I gently swirled the fudge for that gooey marbled effect.
I baked the bread for about 52 minutes, checking with a toothpick until only a few moist crumbs clung to it. After cooling for 10 minutes in the pan, I transferred it to a rack. The smell alone was enough to make me smile!