Preheat the oven at 180°C and line a baking tray with baking paper. Using a cutter, cut out 8 larger circles of pastry. Using a smaller cutter, indent 4 of the pastry circles to form a round border and brush with egg wash. Place the 4 indented circles on top of the other ones, egg washed side down. Brush the 4 pastry bundles with the egg wash.
Bake for about 25 minutes or until raised and golden. Once cooled, with a thin sharp knife cut around the vol au vent indent and gently push down to hollow out and reserve to top the finished vol au vent with a 'hat'.
For the filling, heat a small pan and melt the butter and oil over a medium-high heat and fry the shallot until soft. Add the garlic, fresh mushrooms and the rehydrated ones and sauté for about 5 minutes. Season with salt and pepper. Deglaze with wine and then add the cream. Simmer to thicken the cream, season well and sprinkle with fresh thyme.
Fill the vol aux vents with the mushroom mixture. Replace the little hat on top and serve warm.
