Preheat oven to 350 degrees. Line a 8-9 inch baking dish with parchment paper.
In a large mixing bowl, add all the base layer ingredients and stir well by hand or with a mixer.
Pour the mixture into the lined dish. Smooth out over the bottom.
Bake at 350 degrees for 15 minutes.
While the base is baking, add all the crumble ingredients to the same large mixing bowl. Toss until crumbly and moist. Set aside.
Also while the base layer is baking, blend the raspberries and coconut sugar in a blender until smooth. (Optional Step: to thicken and reduce a bit, simmer the raspberry mixer over medium heat, in a small sauce pot for 1-2 minutes.)
Pull the base layer from the oven. Pour the raspberry mixture over top. Smooth so it is evenly distributed. Dot the whole raspberries over top. Then add the blueberries. Top with the crumble. (For presentation, you can wiggle a few of the whole berries so that they pop out of the crumble, on top.)
Bake at 400 degrees for 22-25 minutes. Cool at least 20 minutes in the dish before slicing and serving. If adding the white glaze, wait until the bars are mostly cooled, whisk together the frosting with a whisk and drizzle over top the bars. Store leftovers, covered, in the fridge.