Begin by preheating your oven to 350°F (175°C). Lightly grease a 9x5-inch loaf pan with butter or cooking spray, and dust it with flour to prevent sticking. This step ensures the loaf comes out clean and keeps the edges from over-browning.
In a medium-sized bowl, whisk together the flour, baking powder, baking soda, and salt. This helps distribute the leavening agents evenly. In a separate large bowl, cream the softened butter and granulated sugar together until light and fluffy. Add in the eggs one at a time, mixing well after each, and stir in the vanilla extract for added depth.
Gradually add the dry mixture into the wet ingredients, alternating with milk. Start and end with the dry mixture. Stir until just combined—overmixing can make the bread dense. Gently fold in the blueberries last, using a spatula to avoid breaking them apart. If using frozen berries, add them straight from the freezer to minimize bleeding.
In a clean bowl, beat together the softened cream cheese, sugar, egg, and vanilla until smooth and creamy. This layer will bake into a deliciously soft swirl through the center of your bread. Make sure the filling is lump-free for the best texture.
Pour half of the batter into your prepared loaf pan. Spoon the cream cheese mixture on top and spread it out evenly. Then pour the remaining batter over the cream cheese layer, smoothing the top gently. Bake for 50–60 minutes, or until a toothpick inserted in the center comes out clean. Let it cool in the pan for 10 minutes before transferring to a wire rack.
Allow the bread to cool completely before slicing for neat pieces. The cream cheese layer firms up as it cools, making each slice cleaner and more visually appealing. Enjoy it plain or with a light glaze if you want to dress it up.