Place the shortcrust pastry and baking paper in a tart tin (approx. 27 cm in diameter) and firmly prick the base. Distribute the squash, mushrooms and ham on top.
Mix the white wine with all the other ingredients up to and including the eggs, season. Pour the sauce over the vegetables.
Bake for approx. 50 mins. on the bottom shelf of an oven preheated to 200°C. Top with the grapes approx. 15 mins. before the cooking time is up.