Preheat oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan.
Whisk together flour, baking powder, baking soda, and salt.
In a large bowl, beat butter and sugar until fluffy. Add eggs one at a time, then mix in vanilla.
Gradually add dry ingredients and milk, alternating between the two. Stir gently to combine.
Fold in blueberries carefully.
In another bowl, beat cream cheese, sugar, egg, and vanilla until smooth.
Pour half the batter into the pan, add the cream cheese layer, and top with remaining batter.
Bake 50–60 minutes, covering with foil if browning too fast. Cool before slicing.