Preheat oven to 375 degrees. Lay 1 filo sheet on a work surface. Lightly brush it with melted butter, and sprinkle with 1 tablespoon of the nuts. Lay another filo sheet on top, brush with butter and sprinkle with nuts. Repeat the layering process with the remaining sheets, leaving the top sheet plain. Sprinkle the chopped chocolate evenly over the top sheet of filo and then sprinkle with the cocoa powder. Starting from a long side, roll up jelly-roll fashion into a log. Brush with the remaining melted butter. Transfer the strudel to baking sheet. Bake for about 20 minutes, or until golden. Cool on the baking sheet for about 10 minutes. Use a serrated knife to cut the strudel into slices about 1/2" thick. Top each slice with some raspberries and dust with powdered sugar. Garnish with mint sprig. I cannot say for certain how many servings this dessert makes, as that depends upon how thick you choose to slice it. It makes quite a lot though.