Preheat oven to 350°F (175°C). Grease and line a standard loaf pan with parchment paper.
In a bowl, beat cream cheese and sugar until smooth. Add egg and vanilla and mix until creamy. Set aside.
In another bowl, whisk flour, baking powder, and salt.
In a large bowl, whisk melted butter and sugar until combined. Add eggs, milk, lemon juice, lemon zest, and vanilla.
Gradually fold dry ingredients into wet ingredients until just combined.
Toss blueberries with 1 teaspoon flour and gently fold into the batter.
Pour half of the batter into the prepared pan. Spread cream cheese mixture evenly over the batter.
Top with remaining batter and smooth gently.
Bake for 55–65 minutes, tenting loosely with foil after 40 minutes if browning too quickly.
Cool in pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.