Finely chop the onions. Heat oil and 20 g butter, sauté the onions until translucent. Add rice, season with salt. Steam the rice for approx. 2 minutes, stirring constantly. Deglaze with prosecco and let it boil down completely. Gradually add hot chicken stock and stir again and again. Add 2 tablespoon parmesan, cover and cook the risotto over low heat for approx. 20 minutes. Add the butter and the rest of the parmesan. Whip the cream and fold into the rice. Season to taste with pepper and salt.