Butter or grease a 9-inch square pan.

Stir together all-purpose flour, oat flour or ground oats, brown sugar and salt in a large bowl using a fork to combine and remove any lumps. Add melted butter and vanilla and stir until thoroughly combined.

Press dough evenly into prepared pan and freeze 30 minutes.

Combine blackberries, sugar, cornstarch, lemon juice and salt in a 2-quart non-reactive saucepan over medium heat. Stir until mixture comes to a boil and continue to simmer stirring constantly until fruit thickens slightly. Remove from heat.

Preheat oven to 300°F.

Place rolled oats, all purpose flour, hazelnuts, brown sugar, granulated sugar, salt, ginger, cinnamon and orange zest in the bowl of a food processor and process until nuts are coarsely chopped. Pour mixture in bowl and drizzle with melted butter using your hands to combine and make small clumps.

Bake frozen crust at 300°F 40 to 45 minutes or until golden brown and firm to the touch. Remove from oven and increase temperature to 350°F.

Spread 1-1/2 cups blackberry filling over crust and sprinkle evenly with crumble topping creating larger clumps if desired.

Bake about 50 minutes or until golden brown, rotating the pan halfway through the baking time. Remove from oven and cool on a rack 10 minutes. Run a knife around the edge of the pan to prevent the bars from sticking. Cool completely and cut into bars.