Heat the oven to 360°F. Grease a 9x5 inch loaf tin.
Whisk together all wet ingredients in a large bowl. Sprinkle flour, cornstarch (OR extra flour), baking powder and salt on top. Gently fold in, do not overmix!
Fold in blueberries and lemon zest and place the batter in the prepared loaf tin.
Bake for 55-60 minutes, or until a toothpick inserted comes out clean.