Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment leaving a 1-inch overhang for easy removal; lightly grease the parchment.

Toss berries

If using frozen blueberries, do not thaw; toss the berries with 1 teaspoon flour and set aside. This helps prevent sinking.

Combine dry ingredients

In a medium bowl, whisk together 2 1/4 cups all-purpose flour, 3/4 cup granulated sugar, 2 teaspoons baking powder, and 1/2 teaspoon fine salt until evenly distributed.

Mix wet ingredients

In a separate large bowl, whisk 2 whole eggs until lightly beaten. Add 3/4 cup whole milk, 1/2 cup vegetable oil, 1 teaspoon vanilla extract, and 1 tablespoon lemon zest (if using). Whisk until combined.

Combine wet and dry

Pour the dry mixture into the wet ingredients and gently fold with a spatula until just combined — do not overmix. The batter will be moderately thick.

Fold in blueberries

Gently fold the floured blueberries into the batter, distributing them evenly. Reserve a small handful (about 2 tablespoons) for the top if you like berries on the crust.

Transfer to pan

Spoon roughly half of the batter into the prepared loaf pan and spread into an even layer.

Cream Cheese Swirl

Prepare cream cheese filling

In a medium bowl, beat 8 oz softened cream cheese with 1/2 cup powdered sugar until smooth. Add 1 egg yolk and 1/2 teaspoon vanilla extract and beat until fully incorporated and silky. If the cream cheese is very soft, beat briefly to avoid over-warming.

Layer and swirl

Drop spoonfuls of the cream cheese mixture over the batter in the pan, distributing evenly. Spread remaining batter over the cream cheese in dollops. Use a butter knife or skewer to gently swirl the cream cheese through the batter to create a marbled effect—do not over-swirl or you will lose distinct swirls.

Bake and finish

Top and bake

If desired, scatter the reserved blueberries on top and sprinkle 1 tablespoon coarse sugar evenly over the loaf. Bake in the preheated 350°F oven on the middle rack for 50–65 minutes, or until the top is golden and a toothpick inserted into the center (avoiding a cream cheese pocket) comes out with a few moist crumbs but not wet batter. If the top browns too quickly, tent loosely with foil after 30–35 minutes.

Cool in pan

Remove the loaf from the oven and let it cool in the pan on a wire rack for 15–20 minutes. This allows the structure to set and makes removal easier.

Remove and cool completely

Using the parchment overhang, lift the bread from the pan and transfer to a wire rack. Let cool completely (about 1–2 hours) before slicing to avoid a gummy texture from cutting while warm.

Finish

Once cooled, dust the top lightly with 1 teaspoon powdered sugar if desired. Slice into 10–12 pieces and serve. Store tightly wrapped in the refrigerator for up to 4 days (cream cheese filling requires refrigeration).