Preheat oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment paper.
In a bowl, whisk flour, baking powder, baking soda, and salt.
Beat butter and sugar until light and fluffy.
Mix in eggs one at a time. Stir in sour cream, milk, and vanilla extract.
Gradually add dry ingredients to wet mixture. Fold in blueberries gently.
Beat cream cheese, sugar, egg, and vanilla until smooth.
Pour half of loaf batter into pan. Spread cream cheese layer evenly. Add remaining batter on top.
Bake 55–65 minutes or until a toothpick inserted (avoiding center filling) comes out clean.
Cool completely before slicing. Drizzle glaze if desired.