Peel the onions (small ones) and slice into thin rings. Place them in a bowl. Add 1 tablespoon of flour and a bit of paprika, and toss to combine. Heat the oil in a frying pan. Add the onions and fry until golden brown. Coarsely crush the walnuts and fry briefly with the onions. Remove the mixture from the frying pan. Drain on paper towels.
In a large pot, bring salted water to a boil. The pot should be about as wide as the spätzle maker is long.
Chop the spinach very fine. Place the flour in a bowl. Add 1 cup chopped spinach, eggs, a bit of salt and nutmeg, and about 6 tablespoons of cold water. Mix to make a thick dough (a wooden spoon works well for this). Mix vigorously against the sides of the bowl with the spoon until the dough is elastic and bubbles form. If the dough is too dry, add a bit more water; if it is too wet, add a bit more flour.
When the water boils, scoop some dough into the hopper of a spätzle maker, and place the spätzle maker over the pot. Lower heat to a simmer. Slide the hopper back and forth to push the spätzle into the barely simmering water. Repeat until all the dough is used up. Bring water back to a boil, then reduce the heat a bit and wait briefly until all the spätzle have risen to the top. Drain the spätzle in a sieve, reserving a bit of the cooking water.
Heat the butter in a frying pan until it foams. Add the spätzle and shake the pan back and forth to gently coat them with butter. Add the cheese and a bit of the reserved cooking water. Cook until the cheese is nicely melted and stringy.
Season the spätzle with salt and plenty of pepper. Divide among deep plates or serve directly from the pan. Garnish with the fried onion and walnut mixture. TIP Spätzle can be made ahead. Drain and rinse the spätzle with cold water, toss with 1 tablespoon of oil, and refrigerate. If you would like to make classic spätzle, omit the spinach and add a bit more water to the dough instead.
Find more recipe ideas in the cookbook "Delicious Wintertime" (appeared in the publishing company gestalten) https://gestalten.com/products/delicious-wintertime