Finely chop the onion and steam in the warm butter. Add the rice and sauté while stirring until glazed. Pour in the wine and allow to boil down completely.
Add the diced carrots. Gradually add stock, stirring frequently, so that the rice is always just covered with liquid.
Simmer for about 20 minutes until the rice is creamy and al dente. Stir in the butter and saffron, and season. Top with the Hobelkäse and serve.