Preheat oven to 375f . Spray a 9-inch square baking dish with nonstick cooking spray. In a medium bowl, combine flour, baking powder and salt with a fork until combined.
In the bowl of a stand mixer (or using a handheld electric mixer in a separate bowl) beat together oil, egg, sugar and vanilla extract. Alternately add the flour mixture and the half and half to the sugar/oil mixture (ending with the flour mixture.)
Batter will be very thick. Finally, stir in the blueberries, by hand, just until combined.
Spread batter into prepared baking dish.
To make the crumble topping, combine the sugar, flour and cinnamon in a small bowl. Add in the cubed butter.
Using a fork, a pastry cutter, or your fingers, cut the butter into the flour mixture until it reaches a crumbly state.
Sprinkle crumble topping on top of cake batter.
Bake the cake for about 40-45 minutes (until top is golden brown) and an inserted toothpick comes out clean.
Allow to cool for at least 10 minutes before slicing and serving.