Blueberry Crumble Cake

Ingredients for blueberry cake:
150 grams flour 
200 grams castor sugar 
1/2 teaspoon salt 
2 teaspoons baking powder  
80 ml oil 
1 egg
100 ml milk 
1.5 teaspoons vanilla extract 
150 grams of blueberry filling

Ingredients for the crumble:
50 grams demerara sugar
1/2 teaspoon cinnamon
25 grams flour
25 grams butter

Method:
Line a 9-inch round pan with parchment paper and preheat the oven to 165 degrees Celsius. For the crumble, mix brown sugar, melted butter, flour, and cinnamon and set aside. Whisk together oil, milk, egg, and vanilla extract. In a separate bowl, sift together flour, sugar, salt, and baking powder. Add the dry ingredients to the wet and mix well. Pour the batter into a 9-inch pan and add the blueberry filling. Swirl it in the batter with a skewer. Sprinkle the crumble evenly. Bake for 20 minutes or till a skewer comes out clean.