Preheat oven to 350 ℉ (180 ℃).
In a small bowl, mix the milk, lemon, and zest.
In the bowl of the stand mixer with the paddle attachment. Or a medium bowl by hand. Cream the butter and sugar until light and fluffy.
One at a time, add the eggs. Mix after each addition.
Mix in the vanilla and salt, until smooth.
Add in the baking powder, flour and half of the blueberries. Mix until just combined.
Add the rest of the blueberries and the soured milk mixture. Stir to combine.
In lined baking tins, spoon the batter, until almost at the top.
Bake 20-30 minutes, or until a toothpick in the centre comes out clean.
Let cool before adding the vanilla glaze. (Click on the link)