Combine the flour, eggs, 150 ml water, 1 tsp salt, and nutmeg in a large bowl. Beat vigorously for 3–5 minutes until the batter is smooth, elastic, and falls slowly from a spoon. If it is too stiff to push through your spaetzle maker, add water 1 tablespoon at a time.

Let the batter rest for 10 minutes. Meanwhile, bring a large pot of water to a boil and add 1 tbsp salt. Preheat the oven to 180°C (355°F), conventional.

Melt 30 g butter in a frying pan over medium-low heat. Add the sliced onions and cook for approximately 15–20 minutes, stirring occasionally, until golden and tender. Lower the heat if they brown too quickly.

Grease a roughly 2 L ovenproof baking dish with the remaining 10 g butter. Working in batches, press the batter through a spaetzle maker into gently boiling water. Simmer for 2–3 minutes, until the spaetzle float and are cooked through, then lift out with a slotted spoon and drain well.

Layer a third of the hot spaetzle in the baking dish and sprinkle with a third of the mixed grated cheeses. Repeat twice with the remaining spaetzle and cheese. Season with black pepper.

Bake uncovered for 8–10 minutes, until the cheese is melted and the dish is heated through. Avoid extended baking, which can dry the spaetzle.

Top with the golden onions and chopped chives. Serve immediately with a green salad if desired.