Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment. In a large bowl, whisk the flour, sugar, baking powder, baking soda, and salt. Remove 1 tablespoon of the dry mixture and toss with the blueberries.

Add the melted butter, sour cream, eggs, and vanilla to the dry ingredients. Stir just until combined; a few lumps are fine.

Gently fold in the flour-coated blueberries.

Scrape the batter into the prepared pan and smooth the top. Sprinkle with coarse sugar if desired. Bake for 50 to 55 minutes, until a toothpick inserted in the center comes out clean.

Cool the cake in the pan for 15 minutes, then lift out and cool completely on a rack before slicing.