Preheat your oven to 325F / 170C. Line a loaf tin with parchment, or grease VERY well. Whisk together the flour, baking powder and salt in one bowl and set aside.
1¾ cups all purpose flour, 2 teaspoons baking powder, ¼ teaspoon salt
Add the butter and granulated sugar to another bowl. Cream together until pale yellow and well combined.
¾ cup butter, ¾ cup granulated sugar
Beat the eggs, and slowly add to the butter and sugar. Add in two or three increments, fully combining before adding more.
2 eggs
Stir in the vanilla and lemon zest.
1 tablespoon vanilla extract, zest of two lemons
Add half of the flour and milk and fold in, before adding the remaining flour and milk, combining so no dry flour is left.
⅔ cup milk
Fold in the blueberries.
1 cup blueberries
Pour the cake batter into the prepared loaf tin.
Bake for around 1 hour, until golden brown and an inserted toothpick comes out clean.
Take the cake out of the oven and rest for 10 minutes before removing it from the tin and placing it on a cooling rack. Let cool completely before glazing it.
Whisk together the lemon glaze ingredients and drizzle over the cake.
1 tablespoon sour cream, juice of ½ lemon, 1 cup confectioners' sugar