Heat oven to 200C/fan 180C/gas 6. Heat oil in a large pan and cook shallots and garlic for 2-3 mins until softened. Stir in mushrooms and courgettes and cook over a high heat for 5-7 mins until golden.
Stir in the rice and cook for 2 mins, then add wine and cook for 3 mins until the liquid has evaporated. Add a ladleful of hot stock and cook, stirring constantly. Continue in this way until all the stock has been used up. Stir in the tarragon, cheese, crème fraîche, pesto and walnuts and plenty of seasoning. Cool.
Fill a 900ml/1½pt pie dish with the rice mixture. Brush the edge of the dish with water. Roll out the pastry on a lightly floured surface and use to cover the filling, trimming the edges and pressing down well to seal. Brush with milk, place on a baking sheet and bake for 20-25 mins until crisp and golden.
Recipe from Good Food Vegetarian Christmas magazine, December 2006