Preheat oven to 350°F (175°C). Grease and line a 9x5-inch loaf pan with parchment, leaving an overhang for easy removal. In a medium bowl whisk together 2 cups all-purpose flour, 1 tsp baking powder, and 1/2 tsp salt; set aside.

Wet mix

In a large bowl whisk or beat together 1/2 cup melted cooled unsalted butter and 3/4 cup granulated sugar until combined. Add 2 large eggs, one at a time, mixing until smooth. Stir in 1 tsp vanilla extract and 1/2 cup milk until incorporated.

Combine

Fold the dry ingredients into the wet ingredients gently with a spatula until just combined; do not overmix. If batter seems very thick, add up to 1–2 tablespoons of milk to reach a spreadable loaf-batter consistency.

Prepare blueberries

Toss 1.5 cups blueberries with 1 tablespoon of flour (reserved from the dry mix) or a dusting of flour to prevent sinking. Gently fold the blueberries into the batter, reserving about 2 tablespoons for topping if desired.

Cream Cheese Swirl

Make filling

In a medium bowl beat 8 oz softened cream cheese with 1/4 cup powdered sugar, 1 egg yolk, 1/2 tsp vanilla extract, and 1/2 tsp lemon zest (if using) until smooth and lump-free. Scrape down the sides to ensure it's creamy.

Layer

Spoon about half of the blueberry batter into the prepared loaf pan and spread to an even layer. Dollop half of the cream cheese mixture in lines over the batter. Spoon the remaining batter on top gently, then drop the remaining cream cheese mixture in several dollops across the top. Use a thin knife or skewer to swirl the cream cheese into the batter; avoid over-swizzling—aim for visible swirls.

Finish & Bake

Top and bake

If using, sprinkle 1 tbs coarse/turbinado sugar and the reserved additional 1/4 cup blueberries evenly over the top. Bake in the preheated 350°F oven for 50–65 minutes, or until the top is golden and a toothpick inserted into the center (avoiding cream cheese pockets) comes out with a few moist crumbs but not raw batter. If the top browns too quickly, tent loosely with foil for the last 10–15 minutes.

Cool

Remove the loaf from the oven and let cool in the pan on a wire rack for 15 minutes. Using the parchment overhang, lift the bread out and transfer to the rack to cool completely (at least another 45 minutes) before slicing to allow the cream cheese to set and prevent squishing.

Storage

Store leftovers covered in the refrigerator for up to 4 days (cream cheese requires refrigeration). Bring slices to room temperature before serving or serve chilled.