Preheat the oven to 400°F (200°C OR 190°C for fan ovens).
Place the cubed root vegetables on a baking tray and drizzle with 1 tablespoon of the olive oil.
Mix together the onion salt, garlic powder, paprika and pepper to taste.
Shake over the root vegetables.
Stir the vegetables to coat with the oil and seasonings and put in the oven.
Set the timer for 15 minutes.
Meanwhile, heat the remaining tablespoon of olive oil in a deep frying pan with a lid.
Sauté the onion until it begins to soften a little.
Add the ground beef and cook, breaking the meat up as you go, until the meat is browned.
When the timer goes off for the vegetables, remove the pan from the oven, turn the vegetables and return the pan to the oven. Set the timer for another 10 minutes.
Stir in the carrots into the meat mixture in the saucepan and shake the cornflour over top of the pan.
Add the stock, a little at a time, stirring constantly, until the meat has a bit of gravy around it.
Cover the frying pan and simmer, adding a little stock if necessary for a fairly thick gravy. .
Put the meat mixture into a 13 x 9 inch baking dish or 4 smaller baking dishes.
Top the meat mixture with the roasted root vegetables.
Place the baking dish or smaller baking dishes on a baking sheet.
Reduce the oven heat to 375°F (190°C or 180°C for fan ovens).
Place the cottage pie(s) in the oven on the baking sheets and bake for 15 to 20 minutes until the mixture is bubbling and the vegetable topping has nice crusty edges (but isn't burned).
Serve the cottage pies with green vegetables.