Preheat oven to 350 F. Line an 8 x 8-inch pan with parchment paper.
In a medium bowl, whisk together flour, oats, brown sugar, cinnamon and salt.
Stir in melted butter and egg yolk. Continue stirring until it becomes a crumble mixture.
Reserve 1 cup of the crumble mixture and set aside. Add the remaining mixture to the baking pan, packing it down into the pan.
In a medium bowl, combine the blueberry mixture ingredients until the blueberries are well coated.
Pour blueberry mixture on top of the crumble base, then sprinkle the remaining 1 cup of oatmeal crumble on top.
Bake for 45-50 minutes or until blueberries are bubbling and crumble is golden brown.
Cool completely before serving.