Take the butter and sugar in a bowl and cream it with an electric whisk for a few minutes.
Add one egg at a time and whisk it until it is evenly mixed.
Now add the vanilla extract and half of the flour in and give it another whisk.
Add the milk into the bowl and shift in the remaining flour, salt and baking powder into the bowl.
Take a spatula and mix everything gently until all the dry flour in incorporated into the dough.--see next step for tip about blueberries!
Add all the blueberries and give it another mix. Tip: if you have trouble with blueberries sinking in your cake, give them a quick shake into the dry mixture to coat.
Pour the batter into a greased and lined cake pan.
Now take the crumble and evenly dust it all over the top of the batter.
Tap the pan gently on the table/counter to get rid of any air bubbles.
Place the cake pan in a preheated oven at 350 degrees (180 degrees Celsius) for about 60 minutes or until a skewer inserted into the middle of the cake comes out clean.
Let the cake cool complete and enjoy!