Step 1: Preheat oven to 350°F (175°C) and grease a 9×5-inch loaf pan.
Step 2: In a medium bowl, whisk together flour, baking powder, and salt; set aside.
Step 3: In a large bowl, beat butter and sugar until light and fluffy, about 2-3 minutes.
Step 4: Add eggs one at a time, beating well after each addition, then mix in vanilla and lemon zest.
Step 5: Gradually add flour mixture alternating with milk, mixing just until combined.
Step 6: Gently fold in blueberries until evenly distributed throughout the batter.
Step 7: In a separate bowl, beat cream cheese until smooth, then swirl it into the batter using a knife.
Step 8: Pour batter into prepared loaf pan and bake for 50-60 minutes until a toothpick inserted comes out clean.
Step 9: Let cool in pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.