- Preheat oven to 160 °C (320°F) with the fan on (see note 1 if you don't have a fan function) and line an 8.5x4.5inch loaf tin (I like to lightly grease the tin before lining it so that the baking paper sticks better). 
- In a bowl sift together your flour, cornstarch, baking powder and salt. Using a whisk or fork, mix until well combined. Set aside for now. 
- In a small bowl combine the warm milk and lemon juice. Mix until well combined and then set aside for now. It will start to curdle, which is normal.  
- In a large bowl cream together the butter, vegetable oil, sugar and lemon zest for 2 minutes until it's light and fluffy.  
- Next add in the eggs one at a time, mixing well in between each addition.  
- Next add in half of the milk/lemon juice mixture from earlier and mix until well combined. Once combined, take any remaining batter off of your mixer attachment/s and set aside as the rest of the mixing will be done by hand.  
- Next add in half of your premixed dry ingredients to your wet mixture, and gently fold it in with a spatula until just combined. Then add in the remaining milk/lemon juice mixture, and fold that in until just combined. Lastly, add in the remaining dry ingredients and gently fold until just combined. Do not overmix (see note 2). 
- Pour the batter into the loaf tin, evenly spread it out and then bake for 1 hour, or until a skewer or butter knife comes out clean.  
- Once baked, allow it to cool for 15 minutes in the loaf tin, and in the meantime prepare the lemon syrup.