Step 1: Preheat your oven to 325°F (160°C). Grease and flour a 9x5-inch loaf pan or a 10-cup Bundt pan, tapping out any excess flour.
Step 2: In a large bowl, cream together the softened butter and granulated sugar with an electric mixer until light and fluffy, about 3-5 minutes.
Step 3: Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
Step 4: In a separate medium bowl, whisk together 2 3/4 cups of the all-purpose flour, baking powder, and salt.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream, beginning and ending with the dry ingredients. Mix until just combined; be careful not to overmix.
Step 6: In a small bowl, gently toss the blueberries with the remaining 1/4 cup of flour. This helps prevent them from sinking.
Step 7: Gently fold the floured blueberries into the cake batter.
Step 8: Pour the batter into your prepared pan and smooth the top.
Step 9: Bake for 60-70 minutes for a loaf pan, or 70-85 minutes for a Bundt pan, or until a wooden skewer inserted into the center comes out with moist crumbs. (Baking time may vary; check for doneness around the 60-minute mark for loaf pans).
Step 10: Let the cake cool in the pan on a wire rack for 15-20 minutes before inverting it onto the rack to cool completely.
Step 11: While the cake cools, prepare the glaze: In a small bowl, whisk together the powdered sugar, 3-4 tablespoons of fresh lemon juice, and 1 tablespoon of lemon zest until smooth. Add more juice if needed to reach a pourable consistency.
Step 12: Once the cake has cooled completely (or is just slightly warm), drizzle the lemon glaze evenly over the top. Let the glaze set before slicing and serving.