1. Place 2 cups of the oats in a food processor and pulse until the oats resemble fine oat bran. Set aside.

2. Preheat the oven to 375 degrees F.

3. In the bowl of a standing mixer fitted with the paddle attachment, combine the reserved oat flour, the remaining 3 cups oats, and the brown rice syrup, ¼ cup of the maple syrup, olive oil, salt, and vanilla until thoroughly combined, about 3 minutes.

4. Firmly press two-thirds of the dough onto a 9- by 12-inch baking sheet. Bake until light brown, about 15 minutes.

5. While the dough is baking, combine the berries, corn flour, and the remaining ¼ cup of the maple syrup in a medium-size bowl.

6. Evenly distribute the berry mixture over the baked oat crust. Crumble the remaining one-third of the dough over the berries, pressing it down firmly. Bake until a golden crust forms, about 40 minutes.