Preheat the oven to 350 degrees F. Spray a 24-cup mini muffin pan with nonstick cooking spray.
Put the shelled pistachios and sugar in a food processor. Pulse a few times to break up the pistachios and then process until the mixture resembles sand, about 30 seconds. Transfer the pistachio mixture to a large bowl. Whisk in the gluten-free baking flour, baking powder and salt.
Whisk the pistachio oil, almond milk and vanilla in a small bowl. Whisk the wet ingredients into the dry ingredients. Whisk in the egg whites. Gently fold in the crumbled frozen raspberry pieces with a rubber spatula. Evenly divide the batter between the muffin cups. Bake until a toothpick inserted in the middle of a teacake comes out clean, 10 to 12 minutes.
Remove to a wire cooling rack and serve.
Frozen raspberries crumble into small pieces easily, making them perfect for these mini bite-size treats. You can also use fresh raspberries, but be careful not to crush them. If they release too much juice, it may make the batter soggy.