Step 1 : Boil water in a saucepan. When the water is boiling, add the yellow chanterelles and onion slices. Let them in for 5 minutes. Then, withdraw the mushrooms and the onion with a little colander.
Step 2 : Add the glass of marsala in the still boiling water. Let the mixture reduce until 50% of the whole liquid had disappeared. Add the sour cream. Let the mixture boil while you are beating with a cooking whisk. Add the basil leaves.