Preheat the oven to 375. Line a baking sheet with parchment paper.
Roll out your puff pastry to 12 x 12 inches. Score border of puff pastry. Brush with egg yolk mixed with 1 Tbsp water. Using a fork, prick pastry all over, keeping them about 2" apart.
Bake in the oven, on the middle rack, 18 to 20 minutes, or until puffed and golden brown. Allow to cool completely.
Spread mascarpone mixture across top leaving 1 cm border around the edges. Scatter berries over the mascarpone. Garnish by dusting with icing sugar and fresh basil or mint.