Prep the pan and oven: Heat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal. Lightly flour the sides.

Mix dry ingredients: In a medium bowl, whisk 2 cups all-purpose flour, 1 1/2 teaspoons baking powder, and 1/2 teaspoon kosher salt. Set aside.

Cream the butter and sugar: In a large bowl, beat 1 cup unsalted butter and 1 cup granulated sugar on medium-high until pale and fluffy, about 3 minutes. Scrape the bowl.

Add eggs and flavorings: Beat in 3 large eggs one at a time, mixing well after each. Stir in 1 tablespoon finely grated lemon zest, 2 tablespoons fresh lemon juice, and 1 teaspoon vanilla.

Add sour cream and dry ingredients: Mix in 1/2 cup sour cream until just combined. Add the dry ingredients and mix on low until incorporated. Do not overmix.

Toss blueberries: In a small bowl, gently toss 1 1/2 cups blueberries with 1 tablespoon flour. This helps keep them from sinking.

Fold and fill: Fold the blueberries into the batter with a spatula. Transfer the batter to the pan and smooth the top. If you like, dot a few extra blueberries on top.

Bake: Bake 55–70 minutes, until the top is golden and a toothpick inserted in the center comes out clean or with a few moist crumbs. If the top browns too quickly, tent with foil around the 45-minute mark.

Cool: Let the cake cool in the pan for 15 minutes, then lift out using the parchment and cool completely on a rack.

Glaze: Whisk 1 cup powdered sugar with 2–3 tablespoons lemon juice (and a splash of milk or cream if you want it creamier) until smooth and pourable. Drizzle over the cooled cake. Let set before slicing.