In a separate bowl, whisk together flour and baking powder
In the bowl of a stand mixer with the paddle attachment, cream together the butter and sugar until light and fluffy (2-3 minutes)
Add eggs one at a time - make sure the mixture is combined really well
Stir in the flour and milk, alternating between each - two additions of each, ending with flour
Mix for 3-4 minutes until well combined - the longer you mix this, the better!
Fold in vanilla
Pour the batter into a parchment paper lined 9"inch cake pan.
Add blueberries on top of the batter - put them in a bowl with a few spoonfuls of flour to coat them. It helps them to not sink to the bottom.
MAKE THE CRUMBLE TOPPING
In a separate bowl, combin flour, brown sugar, cinnamon, salt and melted butter. Use a spatula to mix the crumb together. Then use your hands to form large clumps of crumbles.
Sprinkle crumble over entire top of cake. Make sure it's evenly distributed around edges and middle.
Bake at 350 for 40-45 minutes or until a knife comes clean out of the middle of the cake