Preheat oven to 350°F (177°C). Lightly grease a 9x5 loaf pan and set aside.
In a small bowl, stir together the blueberries, sugar, lemon juice and cornstarch.
Transfer filling to the prepared baking pan and spread into an even layer.
In a separate bowl, stir together the sugar, flour, baking powder, and salt for the topping.
Mix in the melted butter plus the vanilla extract until it comes together into a thick, crumbly dough.
Break the topping into small pieces and scatter them over the blueberries.
Bake on the center rack for 35-40 minutes or until the topping is golden and the filling is bubbling around the edges.
Remove from the oven, place on a cooling rack, and allow to cool for at least 5 minutes before serving.
Serve warm with vanilla ice cream!
Cover leftovers tightly and store in the refrigerator for up to 4 days.
