Preheat oven to 200°C.
Melt the butter in a large saucepan over medium heat. Add the onion, carrot and celery and cook for 4-5 minutes or until softened. Do not brown.
Add the thyme, mushrooms and broccoli and continue cooking for 4-5 minutes then stir through the zucchini and peas. Cook for another minute.
Stir the flour into the pan and continue stirring for a minute until the vegetables are fully coated.
Pour in the stock and bring to the boil, stirring to avoid lumps as the sauce thickens. Add the cream, salt and pepper, cook for another 2-3 minutes and then remove from the heat and set aside for 5 minutes.
Spoon the pie mixture into four 1 1/2 cup ovenproof ramekins and top with spoonful's of mashed potato. Dollop a little butter on the top of each pie.
Transfer to the oven and bake for 15 minutes or until pies are golden. Serve immediately.