Wash the pumpkin, peel it if necessary, cut it into pieces and grate it very coarsely on a vegetable slicer. Chop the onion and garlic, sauté in oil, add the pumpkin rasp and sauté for another 5 minutes. Then mix with salt, pepper and lots of finely chopped garden herbs (to taste) and let cool.
For the sauce, sweat the flour with the butter and deglaze with milk and cream. Bring to the boil while stirring, remove from heat and let cool down a little. Then stir in the grated cheese, sour cream and egg yolk, stir in salt, pepper, nutmeg, possibly garlic and again a lot of finely chopped garden herbs to taste. Finally, carefully fold in the egg whites with a whisk.
Put the vegetables in a greased casserole dish and pour the cream and cheese sauce over it. Bake in a preheated oven at 180 degrees top / bottom heat (160 degrees circulating air) for about 25-30 minutes.
A Hokkaido or a yellow hundredweight is perfect here.