Place the dumplings in a pot with plenty of cold salted water. Bring to the boil and let it boil for 1 minute. Then let it simmer at low heat for 15 minutes. Meanwhile, clean, wash and slice the tomatoes and zucchini.
Wash the basil, dab dry and cut into fine strips, except for a little to garnish. Rinse dumplings briefly under cold water, drain well and allow to cool slightly. Remove dumplings from the cooking bag and cut into 4 thick slices.
Place the tomatoes and courgettes in a greased gratin dish (approx. 24 cm Ø) in alternating fan-shaped layers. Scatter the basil strips in between. Season gratin with salt and pepper. Pour cream over it and sprinkle it thickly with parmesan.
If necessary, spread a few flakes of butter on the gratin and bake in a preheated oven (electric range: 200 °C/ gas: level 3) for approx. 30 minutes. Serve sprinkled with remaining basil leaves and parmesan shavings as desired.