Heat the oven to 190°C. Roll out the pastry on a lightly floured surface and use it to line a deep 22cm flan tin or a rectangular tin. Let the edges overhang. Chill in the fridge or freezer for at least 15 minutes.
Line the tart case with baking parchment and fill it with baking beans. Place on a baking tray, then bake for 15-20 minutes. Re- move the beans and parchment, then return to the oven for another 5 minutes to cook the base. Remove, then reduce the oven temperature to 160°C.
Heat the oil in a large frying pan and cook the mushrooms for 1 minute. Add the spinach, cook for 3 minutes more or until wilted down. Combine the Irvine’s Eggs with the milk and cream in a jug and season well. Build up the tart by sprinkling the cheese onto the base, then scatter over the vegetables and pour over the cream and egg mix. Place the tomatoes over the top, then bake for 40-45 mins or until set. Remove from the oven and allow to cool. Trim the pastry edges and serve in slices, garnished with fresh basil.