Heat oven to 200C/fan 180C/gas 6. Oil a non-stick 12-hole bun tin and line holes with two strips baking parchment, to form a cross. Put the mushrooms in a bowl and pour over hot vegetable stock. Leave for 20 mins, then strain, reserve the stock and chop the mushrooms, if large.
Heat oil in a pan, add onion and fry for 5 mins until softened. Add the pine nuts and fry until lightly toasted. Add the garlic, rice and cook for 2 mins.
Tip in wine, let it bubble, then add the reserved stock, mushrooms and bring to the boil. Reduce heat, cover and simmer for 10 mins, until the rice is just cooked. Remove from heat and cool, then stir in the egg, basil, pepper, and salt, if using.
Fill the tins with stuffing, sprinkle over parmesan. Bake for 20-25 mins, until golden on top. Cool in the tins, or for 5 mins if serving straight away. Remove by pulling up the parchment crosses. Make up to two days ahead. Reheat on an oiled baking sheet, at 200C/fan 180C/gas 6 for 10 mins.