Pre-heat your oven to 320°F. Generously butter 24 mini muffin cups (or 12 large, or 12-16 friand molds).
In a large bowl, combine the flour, baking powder, ground almonds/hazelnuts/pistachios and icing sugar. Whisk to combine.
In a medium sized bowl, whisk the egg whites until very foamy.
Add the melted butter, vanilla and foamy egg whites to your dry ingredients. Fold with a spatula until well combined.
Spoon the batter into your prepared pans, filling them ½ to ¾ of the way full.
Sprinkle some slivered or chopped pistachios on top of each mold. Place 2-3 raspberries on top of each and press them down slightly just so they stick (I'd recommend 2 raspberries in the mini pans, 3 or 4 in the bigger ones).
Bake for 15-20 minutes, until the tops of the cakes are springy and a toothpick inserted into the centre comes out clean.
Let the cakes cool slightly in their pans before moving them to a wire rack to cool completely.
Dust with icing sugar and serve.