Heat your oven to 180°C (160°C fan).
Line your baking tin with baking paper.
Make sure the paper covers all sides.
This stops the cake from sticking later.
Beat the butter and sugar together well.
Use an electric mixer for best results.
Mix until the mixture looks pale and fluffy.
This takes about 3-4 minutes of beating.
Crack the eggs into the bowl one by one.
Beat well after adding each egg.
This stops the mixture from splitting.
Add vanilla extract and mix it in.
Sift the flour and baking powder together.
Gently fold into the wet mixture.
Add the milk to loosen the batter.
Don't overmix or the cake becomes tough.
Gently fold most blueberries into the batter.
Save some for the top decoration.
Be gentle so berries don't burst completely.
Pour the batter into your prepared tin.
Spread it evenly with a spatula.
Scatter remaining blueberries on top.
Bake for 40-45 minutes until golden.
A skewer should come out clean.
Let the cake cool in the tin.
Transfer to a cooling rack after 10 minutes.
Cut into squares when completely cool.
Dust with icing sugar if you like!