Preheat oven to 350°F (175°C) and grease a loaf pan well, lining it with parchment if possible.

In a mixing bowl, cream the softened butter and granulated sugar together until it looks lighter and fluffy, about 3 to 4 minutes.

Add the eggs one at a time, mixing well after each addition. Scrape the sides of the bowl as needed.

Mix in the lemon zest, lemon juice, and vanilla extract.

In a separate bowl, whisk together the flour, baking powder, and salt.

Add the dry ingredients to the wet mixture in two or three additions, alternating with the sour cream and a splash of milk. Stop mixing as soon as no dry flour remains.

Toss the blueberries with a tablespoon of flour, then gently fold them into the batter.

Pour the batter into the prepared pan, smoothing the top.

Bake for 55 to 70 minutes, checking with a toothpick until it comes out with a few moist crumbs. If the top browns too quickly, tent with foil.

Allow the cake to cool in the pan for about 15 minutes, then transfer it to a wire rack to cool completely before slicing.