1-First, preheat your oven to 350 degrees Fahrenheit and prepare your raspberries. Place the frozen raspberries in a large colander, rinse with warm water, and drain for about an hour until softened and most liquid is removed. Then, mix the raspberries with 1/2 cup granulated sugar, 2 tablespoons flour, 1 tablespoon cornstarch, and the juice of one lemon to create the filling.

2-Next, in a separate bowl, combine 3 cups rolled oats, 3 cups flour, 2 cups loosely packed brown sugar, 1 teaspoon baking powder, 1 1/2 cups melted butter, and 1/2 teaspoon salt to form the crumble mixture. Press two-thirds of this mixture into the bottom of a 9×13 inch pan lined with parchment paper and bake for 10 minutes.

3-Spread the raspberry filling evenly over the baked crust, then sprinkle the remaining crumble mixture on top. Bake for another 25 to 30 minutes until it’s golden and bubbly. Finally, remove from the oven and let it set, ideally chilling for several hours to make slicing easier the bars can be eaten warm for a soft, fruity twist. For dietary adaptations, use plant-based butter for vegan versions or gluten-free flour blends as needed.