Making individual pot pies is a nice touch for a dinner party. Or leave out the pastry and simply serve the mushroom sauce on rice, mash or pasta with grated parmesan.
Soak the onions in boiling water for 20 mins. In the meantime, peel and cube the potatoes and keep to one side. Once soaked, peel and trim the roots off the whole baby onions and cook in the olive oil in a pot with the leeks, celery and carrots over medium heat for about 20 minutes until the vegetables begin to caramelise. Stir frequently to prevent scorching.
Add the mushrooms and herbs and cook for a further 10 minutes before adding the red wine, stock, tomato concentrate and potato chunks. Put on the lid and simmer over medium heat for 20–25 minutes until the sauce has thickened and all the vegetables are tender but still holding their shape. Stir well and season to taste.
Fill 4 to 6 pot pie dishes or 1 large pie dish three-quarters full with the mushroom stew and allow to cool completely. In the meantime, preheat the oven to 200 °C.
Cut circles 1 cm wider than the diameter of the pie dishes from the pastry and use to cover the pies, crimping the edges. Cut one or two vents in the pastry lids for steam to escape, and brush with a little beaten egg to ensure a golden brown colour.
Bake in the centre of the oven for 20 minutes or until the pastry looks puffy and golden brown all over. Serve piping hot.