Preheat oven to 375 °F (177 °C).
Make crumble topping: Using a hand mixer or stand mixer, mix together butter, brown sugar, and vanilla until incorporated. Add pecans, flour, cinnamon, and salt to the bowl and mix together with a spatula. Once the mixture begins sticking together, use your hands to continue mixing until small clumps are formed.
Make the blueberry filling: Add blueberries to an appropriately sized baking dish based on the number of portions. In a small bowl, combine salt, cornstarch, and brown sugar. Sprinkle the cornstarch mixture over the top of the blueberries.
Assemble: Add the crumble topping in a layer over the blueberries.
Place in the oven and bake for 25-30 minutes or until the blueberries are bubbling in the center of the baking dish and the topping is beautifully golden brown. See note. Let cool down for 5 minutes before portioning.
Serve: Enjoy blueberry crumble with a scoop of vanilla ice cream and milk.