Chop the onion and mushrooms very finely. You can also use a food processor or the pulse mode in mixie. Melt the butter in a pan.
Add the onions and mushroom and saute it till it is soft and cooked. Add the flour (maida) and fry for a minute to get rid of its raw smell.
Add the milk, chicken stock, pepper powder and salt. After it comes to a boil, reduce the flame and let it simmer for 5-10 minutes.
The soup will get thickened by now. Add the oregano and cream. Mix and switch off.
( You can use italian seasoning instead of oregano. Health consious people can skip the cream.) Garnish with parsley/cilantro leaf or some green onions or some grated cheese or some croutons.
Serve hot with some toasted bread. Its a easy to make, filling and satisfying meal for a cold or rainy day.