Directions for the crust

Grease a 9-inch square pan or line your pan with parchment paper.

In a large bowl, stir together flours, brown sugar and salt until mixture is smooth and lumps are gone. Add melted butter and vanilla and stir until combined.

Press dough evenly into the prepared pan and place in the freezer for 30 minutes.

Directions for the blackberry filling

In a medium saucepan over medium heat, combine blackberries, sugar, cornstarch, and lemon juice. 

Bring mixture to a boil, stirring constantly. Reduce heat and continue to stir while simmering until fruit thickens slightly. Remove from heat and set aside.

Directions for the topping

Place oats, flours, sugars and salt in a food processor {or blender} and process until oats are partially ground. 

Move mixture to a large mixing bowl and add melted butter, stirring until small clumps form. Set aside.

Preheat the oven to 300F.

Remove the crust from the freezer and bake frozen crust for 45 minutes or until golden brown. Remove from the oven and increase oven temp to 350 F. 

Spread blackberry filling over crust and sprinkle evenly with crumb topping.

Bake for 45-50 minutes or until golden brown, rotating the pan halfway through baking. Cool completely before cutting into bars.