01 - Preheat the oven to 400°F.
02 - Heat olive oil in a large skillet over medium heat. Add diced onion and cook for 4-5 minutes until softened. Add garlic and cook for 1 minute.
03 - Stir in flour and cook for 1 minute, stirring constantly to form a roux.
04 - Gradually pour in vegetable stock, stirring to avoid lumps. Add cream and dried herbs. Simmer until slightly thickened, about 2-3 minutes.
05 - Add leftover roast vegetables to the sauce. Stir to combine and cook for another 2-3 minutes. Season with salt and pepper to taste.
06 - Transfer filling to a 9-inch pie dish or baking dish.
07 - Roll out puff pastry to fit the dish. Drape pastry over filling, trimming excess. Press edges to seal and cut small slits in top for steam escape.
08 - Brush pastry with beaten egg for golden finish.
09 - Bake for 25-30 minutes until pastry is golden brown and crisp.
10 - Let cool for 5 minutes before serving.