Preheat oven to 400 degrees, place rack in the center of the oven and line baking sheet with parchment paper or a baking sheet. 

Cut the chilled sheet of puff pastry into 6 equal pieces and place on the lined baking sheet for assembly.

Using a pastry brush or your finger, brush the outer ½ inch of pastry all the way around each tart. Using your index finger and thumb gently press the corners together to form a fluted effect. 

Sprinkle the cookie crumbs into the center of each tart, top with the strawberries and raspberry on each tart, making a design if you wish. 

Top each tart with a sprinkle of sugar, a squeeze of lemon juice, and a cube of butter. 

Bake in the oven for 12 - 15 minutes until golden brown. Set on a wire rack to cool. 

Fill a plastic bag with the nutella. Cut the corner and drizzle nutella over the tarts. 

Top with a sprinkle of powdered sugar and enjoy!