Preheat oven to 190ºC (170º fan assisted)/375ºF/ Gas M 5
Melt the butter and add the garlic and some of the chopped parsley.
Open out the filo pastry and slice the stack of sheets in half across it’s length to give 2 stacks of rectangular pastry. Lay one sheet of pastry on a work surface, brush with the garlic butter and then lay a second piece on top, with corners offset. Brush again with butter.
Place one mushroom stalk side up in centre of the brushed filo and bring up the filo, scrunching or folding gently to form a border around the sides of the mushroom. Place on a lined baking sheets and continue with remaining pastry and mushrooms.
Brush tops of mushrooms generously with the garlic butter and bake for 12-15 minutes until pastry is dark golden brown and mushrooms cooked.
Drizzle with any remaining butter and scatter with remaining chopped parsley.