Preheat your oven to 350°F (175°C).
Grease your loaf pan with butter or non-stick spray.
In a large mixing bowl, combine creamy peanut butter and granulated sugar. Beat until smooth. Add eggs one at a time, mixing well. Stir in vanilla extract.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Gradually add the dry mixture to the peanut butter mixture, alternating with milk. Stir until just combined.
Spoon half of the batter into the loaf pan. Drop spoonfuls of Nutella over the batter and swirl with a knife. Top with remaining batter and more Nutella.
Bake for 50-60 minutes, or until a toothpick inserted comes out clean. Cover with foil if browning too quickly.
Let the loaf cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.