Peel the squash (not necessary with the Hokkaido squash. Simply wash it properly and rub it dry), halve, take the seeds out and cut into about 2" (5 cm) slices. Wash the spring onions, rinse and cut in about 1" (3 cm) pieces. Coarsely chop the seeds. Beat the eggs and the sour cream. Grate the Gruyère AOP and add to the mixture. Add salt, pepper and nutmeg.
Heat the oil in a big pan that can be put in the oven. Let the pumpkin seeds and the pumpkin slices cook for about 10 minutes until they soften. Add the onion spring and let cook for a little while. Add the egg-cheese-mix and let on the fire for about 3 minutes, until the egg gets brown on the pan floor. Put the pan on the 350°F (180°C) hot oven and let cook for about 25 minutes until the tortilla is gold-brown