Heat the oil in a skillet over medium heat. Add the sliced mushrooms and cook uncovered until mushrooms are golden and all liquid is absorbed.

Add turmeric powder and stir well. Set aside.

Dissolve flour in the cold milk and set aside.

Melt the butter in a saucepan over low heat. Add the dissolved flour. Stir constantly until mixed and all the lumps are gone, about 2 minutes.

Add salt and pepper. Continue cooking over low heat until sauce begins to thicken, stirring constantly.

Then add the mushrooms to the sauce and mix well. Add more salt and pepper if needed.

Note: For richer sauce, add a few tablespoons of heavy cream.