Preheat oven to 375 degrees.
Lightly butter square or round baking dish. Approx. 8-inches in width.
Prepare the filling. Gently combine blueberries, sugar, juice, cornstarch, vanilla. Try not to burst the blueberries while mixing.
Set berry mixture aside.
Add flour, sugars and butter to a stand mixer with a paddle attachment or by hand.
Stir in the oats and optional nuts.
Pour the berry mixture into the baking dish.
Sprinkle the crumble mixture topping evenly over the fruit mixture.
Bake for 30 minutes or until golden brown.
Many of the blueberries will burst in the heat. Don't worry, that's normal.
Serve with a dollop of homemade whipped cream or scoop of vanilla bean ice cream.