To prepare the bake
Grease the gratin dish with butter. Halve the cherry tomatoes, place in the dish. Halve the courgette, cut into slices, roughly chop the spinach, add both to the tomatoes in the dish. Mix in the tortellini.
Bring the stock to the boil. Tear off and finely chop the basil leaves, add to the stock along with the cheese and cornflour, mix well. Pour the sauce over the vegetables, mix.
Approx. 40 mins. in the lower half of an oven preheated to 200°C, stirring once. Remove from the oven and leave to stand for approx. 2 mins., serve.