01 -
Melt butter in a large skillet over medium-low heat. Add sliced onions and a pinch of sugar, stirring to coat. Cook, stirring every 5–8 minutes, until deep golden and caramelized, about 30–40 minutes.
02 -
Preheat the oven to 220°C. Toss sweet potato cubes with olive oil, salt, and pepper. Spread on a baking sheet and roast for 20 minutes, or until tender.
03 -
Cut the bratwurst lengthwise and remove the filling from the casing. Cook the sausage over medium heat, breaking it up with a spoon, until fully browned and cooked through, 10–15 minutes. Transfer the crumbled bratwurst to a plate lined with paper towels.
04 -
Reduce oven temperature to 200°C. Grease a 23 x 33 cm baking dish or a 30 cm cast-iron skillet. Layer half the cooked spaetzle in the dish, followed by half each of the grated Havarti, Gruyère, bratwurst, sweet potatoes, and caramelized onions. Repeat the layering with the remaining ingredients.
05 -
Bake in the centre of the oven for 15–20 minutes, or until the cheese has melted and the top is lightly golden. Finish with plenty of chopped fresh sage before serving.