Heat the oven to 200°C and defrost the frozen spinach (or defrost later in the microwave).
Peel the sweet potatoes and cut into thin slices. When the sweet potatoes are cut, grease a baking dish with butter or coconut oil.
Then place the slices on the bottom of the baking dish. Once this is done without any gaps (it doesn't have to be perfect), cut the remaining sweet potato slices in half and place them along the edge. And with the cut side down.
Salt and pepper the sweet potatoes, cover with aluminum foil and bake for 15 minutes.
Meanwhile, fry the onion until golden brown. Then add the spinach to the pan and mix together over low heat. Once everything is well mixed, season with salt and pepper. Remove the pan from the heat. Then squeeze the spinach with the help of a sieve, otherwise the quiche filling will have too much liquid.
Then whisk the eggs with the milk, cream of goat cheese, nutmeg, salt and pepper.
After half an hour, remove the quiche base from the oven. Spread the spinach and salmon on top. Then pour the egg mixture over it. If you like, you can spread a little grated feta on top.
After that, the sweet potato quiche goes back into the oven. This time for 20 minutes (covered) and another 20 minutes without cover. Or just until the goat cheese is golden brown.