Instructions

Preheat oven to 375°F.
In a saucepan, melt butter over medium heat.
Meanwhile, in a food processor, grind pistachios with powdered sugar and flour until finely ground but do not go so far as to make a paste.
Add egg whites, melted butter and mix.
Batter can be used immediately or kept refrigerated for up to 3 days.
When ready to bake, butter tiny tart molds or a mini muffin tin and spoon in batter to fill mold 2/3 of the way.
Cut blackberries in half, the long way, and place 1/2 on top of the batter cut side down.
Bake for approximately 15 minutes, until golden brown.
Let cool in molds and gently lift cakes out.

To serve

Sprinkle with powdered sugar and serve the same day.