Peel onion and garlic. Chop both finely. Clean and wash the kale and cut into bite-sized pieces. Peel potatoes and cut them into cubes of about 1 cm. For the noodles, boil 3-4 l salted water (1 teaspoon salt per litre).
Heat the oil in a pot. Fry onion, garlic and potatoes for about 3 minutes while turning. Add stock and simmer for about 8 minutes until the potatoes are firm to the bite. Stir in kale.
Stew covered for about 5 minutes. Season ragout with salt and pepper.
Cook the pasta in boiling salted water according to the instructions on the packet until al dente. Wash the thyme, shake dry and pluck the leaves. Cut the fontina into cubes. Grate the parmesan finely.
Drain the noodles and collect about 5 tablespoons of pasta water. Put the noodles and pasta water back into the pot. Stir in thyme, ragout, fontina cubes and butter. Bring to the boil, season to taste with salt and pepper.
Serve with parmesan.