Preheat your oven to 350°F (175°C).

Grease a 9×5-inch loaf pan and line it with parchment paper, leaving overhang for easy removal.

In a medium-sized bowl, thoroughly whisk the flour, baking powder, and salt until the mixture is well blended and uniform.

Set aside.

In a large mixing bowl, whisk the sugar and eggs until pale and slightly thickened.

Slowly whisk in the oil (or melted butter), milk or sour cream, and vanilla extract until smooth.

Add the dry ingredients to the wet ingredients.

Mix gently just until no dry streaks remain. Do not overmix.

Toss the blueberries with 1 tablespoon of flour.

Gently fold them into the batter so they stay evenly distributed and don’t sink to the bottom.

In another bowl, beat the softened cream cheese until it becomes smooth and creamy.

Add sugar, egg, and vanilla extract.

Beat until creamy and fully combined with no lumps.

Pour ½ of the blueberry batter into the prepared loaf pan.

Gently spread the cream cheese mixture into an even layer over the batter.

Top with the remaining blueberry batter.

Optional: Gently swirl with a knife for a marbled effect.

Bake for 55–65 minutes, or until the top is set and lightly golden.

A toothpick inserted into the center should come out with a few moist crumbs but no wet batter.

If the top browns too quickly, loosely cover with foil during the last 15 minutes.

Allow the loaf to rest in the pan for about 15 minutes before removing it.

Use the parchment paper to carefully lift the loaf out of the pan, then transfer it to a wire rack and let it cool completely before slicing.