Prepare the Peanut Butter Portion:

1. In a medium bowl, whisk together the flour, vanilla instant pudding mix, baking powder, baking soda, and salt. Set aside.
2. In another bowl, whisk together the sour cream, vegetable oil, eggs, vanilla extract, and milk.
3. In a large mixing bowl, beat the brown sugar and peanut butter together until smooth.
4. Gradually add the dry ingredients to the wet mixture, alternating until fully incorporated.

2. Prepare the Chocolate Portion:

1. In a medium bowl, mix the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
2. In another bowl, whisk together the sour cream, vegetable oil, eggs, and vanilla extract.
3. Slowly combine the wet ingredients with the dry ingredients, stirring until smooth. Fold in 3/4 cup of the chocolate chips.

3. Assemble the Loaf:

1. Preheat your oven to 350°F (175°C). Grease two 9”x5” loaf pans.
2. Divide half of the peanut butter batter evenly into each loaf pan, followed by half of the chocolate batter.
3. Use a knife to gently swirl the two batters together, creating a marbled effect.
4. Sprinkle the remaining chocolate chips on top of each loaf.

4. Bake:

1. Place the pans in the oven and bake for 45 minutes.
2. Tent the loaves with foil to prevent over-browning and continue baking for another 20-25 minutes, or until a toothpick inserted into the center comes out mostly clean.
3. Let the loaves cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.