Combine the goat's cheese, herbs, salt and pepper.
Roll out the puff pastry to a few cm thick and cut into 6 equal sized rectangles. Place on a baking sheet lined with baking paper. Note: Serve as smaller appetizers by cutting the pastry into smaller pieces and slightly reduce the baking time.
Spread the goat cheese mixture on each piece of puff pastry leaving a few cm around the edge as a border.
Bake the tarts for 18-20 minutes until they have puffed up and are golden brown around the edges.
Tear the mushrooms into strips (can discard stem or cut into smaller pieces and use)
While the tarts are baking, melt the butter in a frying pan over medium heat and sauté the mushrooms until soft.
When the tarts are baked, top with mushrooms and serve. Salt and pepper to taste.