1. First, cut mushrooms and onions.
2. Pour a little oil into the pot and stir-fry the onion until it is soft and fragrant.
3. Stir-fry onions and serve, and pour a little oil into the pot.
4. Add flour and stir-fry the flour over medium heat until the flour is slightly yellow.
5. Pour in the milk, stir the onion while cooking, and cook for 4 minutes.