For the risotto, peel onions and garlic and dice finely. Dissolve stock in 1 l boiling water. Heat butter in a pot. Fry half of the onions and garlic in it until transparent. Add rice and also fry until transparent.
Add wine and simmer at low heat while stirring until evaporated. Cover the rice with some stock. As soon as the rice has absorbed the broth, pour in some broth again and again. Simmer open at low heat for about 25 minutes, stirring occasionally.
For the ratatouille, clean, wash and dice the vegetables. Wash and chop the sage. Heat oil in a pan with lid. Fry the zucchini, peppers, sage, remaining onions and garlic for about 5 minutes.
Add the tomatoes. Cover and stew for about 5 minutes. Season to taste with salt and pepper.
Grate parmesan. Stir half with mascarpone into the risotto. Season to taste. Pour into a greased casserole dish. Spread the vegetables and the rest of the Parmesan cheese on top. In a hot oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see
manufacturer) bake for about 10 minutes.