Start by preheating your oven to 350°F (175°C). Grease your 9x5-inch loaf pan with a little oil or line it with parchment paper for easy removal.
In a large bowl, whisk together the all-purpose flour, granulated sugar, baking soda, salt, and cocoa powder. Make sure everything is evenly combined for a consistent texture.
In a separate bowl, beat the eggs lightly and add the vegetable oil, apple butter, and vanilla extract. Whisk until the mixture is smooth and well blended.
Pour the wet ingredients into the dry ingredients. Use a spatula or spoon to gently fold and mix until just combined. Be careful not to overmix — a few lumps are okay.
Fold in the chocolate chips evenly throughout the batter. This will create delightful pockets of melted chocolate in every bite.
Pour half of the batter into the prepared loaf pan. Then add dollops of the remaining batter on top. Using a butter knife or skewer, gently swirl the batter to create a marbled effect. This step gives the bread its signature chocolate swirl.
Bake in the preheated oven for about 50-60 minutes. Start checking at 50 minutes by inserting a toothpick into the center — it should come out clean or with just a few moist crumbs. Avoid overbaking to keep the bread moist.
Remove the bread from the oven and let it cool in the pan for 10-15 minutes. Then transfer it to a cooling rack to cool completely before slicing. This prevents the bread from becoming gummy and helps the swirl set beautifully.