Coat a 10-inch baking dish generously with butter, then scatter the raspberries and blueberries on the bottom of the dish.
In a blender, combine the milk ½ cup of the granulated sugar, eggs, vanilla, almond extract, fine sea salt, flour and orange zest. Blend well for about 15 seconds, then let the batter rest for 30 minutes (this step is important).
After 15 minutes, preheat the oven to 400℉.
Pour the rested batter over the berries and sprinkle the remaining ¼ cup of granulated sugar over the top.
Bake for about 45 minutes until the top is puffed and browned and a toothpick into the center comes out clean.
Before serving, using a fine-mesh sieve, sprinkle some powdered sugar over the top.